Add project name to comments

[lkysow]

If projects are configured using an atlantis.yaml with a specific
project name, include that in the output for comments. This is useful
because often the project names are better identifiers than the
directory and workspace names and also because some projects use the
same dir and workspace so the only way to differentiate them is via
their names.

Fixes #353

[codecov]

Codecov Report

Merging #373 into master will increase coverage by 0.05%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #373      +/-   ##
=========================================
+ Coverage   70.25%   70.3%   +0.05%     
=========================================
  Files          62      62              
  Lines        3735    3742       +7     
=========================================
+ Hits         2624    2631       +7     
  Misses        923     923              
  Partials      188     188

Impacted Files	Coverage Δ
server/events/project_result.go	100% <ø> (ø)	⬆️
server/events/markdown_renderer.go	92% <100%> (+0.1%)	⬆️
server/events/models/models.go	89.61% <100%> (+0.56%)	⬆️
server/events/project_command_runner.go	81.74% <100%> (+0.29%)	⬆️

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