Further cleanups, no semantic change

* Add -Wall to cabal
* Apply style changes matching style-guide
* Commented declarations
* Remove redundant whitespace
Handle newline-indent better when inside a type-signature
Add initial contextual menu items and rules
Move context menu code to new file

Allows the user to require context menu functionality wanted
Remove file header message
Add shm/modify-type-constraint

Add new type constraints to a selected 'full' type signature node