Introduce new `mergeable` requirement, in similar vein to the `approved`
requirement. Ran `make go-generate` to update mocks accordingly.
This addresses issue #43.
On startup, make a call to the /version endpoint of Gitlab to get which
version we're running. Then use that version to determine whether we
should use the markdown folding syntax where the code is expandable.
Versions of Gitlab < 11.1 don't support the "Common Mark" markdown
format.
Fixes https://github.com/runatlantis/atlantis/issues/315
Add Apache 2 license and Hootsuite copyright to all golang
files. Add a disclaimer that the files have been modified
hereafter by contributors to this repo in order to abide
by the Apache 2 license requirements.
