Accept comments like
```
atlantis plan
```
So that when a comment is copy-pasted in GitHub and GitHub adds two
newlines, Atlantis still parses that comment.
This change makes things cleaner because there will only ever be one
plan generated in the comment flow. It's okay to make this change
because typing the plan command a couple times isn't too bad AND we're
going to be implementing autoplanning which should handle most of the
times you needed to type plan from before.
Saw in the TF code how they were validating workspace names
and decided to do the same. '..' is actually a valid TF workspace but we
don't support that.
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.
