Add help menu items

[ihumphrey]

Added help menu actions:

• Link to documentation for Xi-CAM2
• Link to create a new issue on the Xi-cam repository
• Non-Modal About dialog that shows the current version and (c) text

Fixes #65

[ronpandolfi]

TODO:

• [x] Add issue template
• [ ] Add contributors to about(?)
• [x] Link to slack(?)

[ihumphrey]

@ronpandolfi Added an issue template (for "bug" type issues), added a link to slack. Somethings we might want to think about:

• Should the Xi-cam repo to be the default catch-all for user-reported issues?
  • Additionally, where should issues be reported for community-contributed plugins reside? How could we hook up the links appropriately?
• Where should questions be redirected to (a question template, slack, forum, ...)?
• Regarding the link to slack, what is our intent for slack? A place for anyone to ask questions? Does it support search well enough to act as a user resource (like a stack overflow or forum type site)?
• It could be nice to automatically try to read in the Xi-CAM log file and attach it to the body of the new issue; this could be too much information right now though as there is only one log file. If there were one per each Xi-CAM run, then it might be more feasible.