* Move webhook to a standalone package under modules

* fix test

* fix comments

* if a filename in a repository contains " or \ the owner can't merge pull request with this files
because "git diff-tree" adds double quotes to that filepath
example: filepath is ab"cd but "git diff-tree" returns "ab\"cd"

now, when the owner click "Merge Pull Request" button the server returns 500
this commit fix it

Signed-off-by: Ilya Pavlov <ilux@cpan.org>

* add -z option to getDiffTree
escape spec symbols for sparse-checkout

Signed-off-by: Ilya Pavlov <ilux@cpan.org>

* go fmt

Signed-off-by: Ilya Pavlov <ilux@cpan.org>

* typo

Signed-off-by: Ilya Pavlov <ilux@cpan.org>

* escape '\'
escape all spaces and '!'

* use regexp.ReplaceAllString()

Signed-off-by: Ilya Pavlov <ilux@cpan.org>

* strings.ReplaceAll was added in go 1.12

Signed-off-by: Ilya Pavlov <ilux@cpan.org>

* add '\' to regexp.MustCompile

Signed-off-by: Ilya Pavlov <ilux@cpan.org>

* fix bug on pull requests when transfer head repository

* add migration and fix lint

* fix tests and add a cache check on LoadBaseRepo

This PR fixes #7598 by providing a configurable way of signing commits across the Gitea instance. Per repository configurability and import/generation of trusted secure keys is not provided by this PR - from a security PoV that's probably impossible to do properly. Similarly web-signing, that is asking the user to sign something, is not implemented - this could be done at a later stage however.

## Features
- [x] If commit.gpgsign is set in .gitconfig sign commits and files created through repofiles. (merges should already have been signed.)
- [x] Verify commits signed with the default gpg as valid
- [x] Signer, Committer and Author can all be different
    - [x] Allow signer to be arbitrarily different - We still require the key to have an activated email on Gitea. A more complete implementation would be to use a keyserver and mark external-or-unactivated with an "unknown" trust level icon.
- [x] Add a signing-key.gpg endpoint to get the default gpg pub key if available
    - Rather than add a fake web-flow user I've added this as an endpoint on /api/v1/signing-key.gpg
    - [x] Try to match the default key with a user on gitea - this is done at verification time
- [x] Make things configurable?
    - app.ini configuration done
    - [x] when checking commits are signed need to check if they're actually verifiable too
- [x] Add documentation

I have decided that adjusting the docker to create a default gpg key is not the correct thing to do and therefore have not implemented this.

* move AddTestPullRequestTask to pull service package from models

* fix fmt

* Change tests to make it possible to run TestGit with 1.7.2

* Make merge run on 1.7.2

* Fix tracking and staging branch name problem

* Ensure that git 1.7.2 works on tests

* ensure that there is no chance for conflicts

* Fix-up missing merge issues

* Final rm

* Ensure LFS filters run on the tests

* Do not sign commits from temp repo

* Restore tracking fetch change

* Apply suggestions from code review

* Update modules/repofiles/temp_repo.go

* extract actions on new pull request from models to pulls service

* improve code

* move code.gitea.io/gitea/modules/pull to code.gitea.io/gitea/services/pull

* fix fmt

* Rename pulls.go to pull.go