Fix #53 - recognize common attributes in the PR title

[wilzbach]

Problem: users don't have the permission to add labels.

The idea is simple: the bot parses the PR title for a pre-approved list, e.g.

[Trivial] -> add "Trivial" label

Currently this function will get checked "open" or edited" events.
Gotchas:

• There wasn't an edited hook payload in the data set (should be similar to open though)
• For now it doesn't remove these added labels (but this is seldom required anyways)