Allows MR authors to have the source branch removed when merging the MR
closes#13191
The location of the checkbox might not be optimal so any feedback is welcome. Any other feedback too obviously.
Screenshot:

See merge request !2801
Update CE code to include some refactor done in EE to do with import url
This is simply updating the code to match EE and avoid further conflicts related to `import_data` and `import_url` changes made on EE only.
See merge request !4223
Create a todo on failing MR build
Implements #14067. I worked on this with @DouweM (any mistakes are mine).
When a build fails for a commit, create a todo for the author of the merge request that commit is the HEAD of. If the commit isn't the HEAD commit of any MR, don't do anything. If there already is a todo for that user and MR, don't do anything.
Current limitations:
- This isn't configurable by project.
- The author of a merge request might not be the person who pushed the breaking commit.
- I haven't tested this with a working CI setup, just with the unit tests below and by modifying my DB directly.
See merge request !3177
Since we eager load everything in lib/ putting ERB code in .rb files
will result in syntax errors. By moving the templates to
./generator_templates we can work around this.
Resolve "Wrong sorting of commit order in MR view?"
!4052 fixed this for the most obvious cases, but there were still some problems.
Here's my test case: I have a branch where I was suffering from an unfortunate
issue. Every other commit I made had its commit date set to one day before it
should have been. (Perhaps my system clock was misbehaving.)
```shell
for i in {1..10}
do
echo $i > $i
git add $i
GIT_COMMITTER_DATE=`date -v -$((i % 2))d` git commit -m $i
done
```
The git CLI still gives me the commits in the right order, but I can see that
the timestamps alternate between two values:
```shell
$ git log --format='%h %ct %p %s' master...HEAD
f0c3108 1463646313 3d38a13 10
3d38a13 1463559913 67f419b 9
67f419b 1463646313 74330c0 8
74330c0 1463559913 56361d7 7
56361d7 1463646313 ba1b60c 6
ba1b60c 1463559913 f91497d 5
f91497d 1463646313 79c5e57 4
79c5e57 1463559913 b953cef 3
b953cef 1463646313 12fc411 2
12fc411 1463559913 835715b 1
```
Unfortunately, GitLab didn't like this _at all_. Here's what the commits on my
MR from that branch looked like:

That's because we were sorting the commits by date, which is safe if they are in
that order anyway. If they aren't, then because Ruby's sorting isn't stable, we
lose even the ordering among the correctly-ordered commits with the same
timestamp.
After these changes (and reloading the MR's diff), this looks like:

The commits view was also wrong, but in a slightly different way. In table form:
| View | Before | After |
| --- | --- | --- |
| Commit list | 10, 8, 6, 4, 2, 9, 7, 5, 3, 1 | 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 |
| MR commits | 10, 2, 8, 4, 6, 5, 7, 3, 9, 1 | 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 |
Closes#12724
See merge request !4208