Omnisharp: smarter solution file finder

When loading the Omnisharp server, YCM tries to find a suitable solution
file to feed it. Instead of giving up when finding multiple solution
files, it now tries to find one named like the edited files' folder at
the solution level, e.g. if we have bla/Project.sln and we are editing
bla/Project/Folder/Whatever/File.cs, we use bla/Project.sln.
Unit test for Omnisharp's smarter solution finder
Unit tests for Omnisharp's smarter solution finder
Merge github.com:nop00/YouCompleteMe
Small stylistic changes
Merge pull request #680 from nop00/master

Omnisharp: smarter solution file finder