Further changes for timestamp display and cleanup

Added "delete all" option at startup
Support displaying timestamp as a date or as a relative time (modified 2 days, 5 hours ago)
Fixed bug that didn't allow quick panel actions if preview was turned off
Fixed bug that didn't save the changes when a history entry was deleted from the quick panel
added delete all and more timestamp options

Added "delete all" option at startup
Support displaying timestamp as a date or as a relative time (modified 2 days, 5 hours ago)
Added command for reset history
Added command for resetting the history

reset_file_history
Use a context handler for file history overlay commands

Instead of using a transient setting in Preferences.sublime-settings,
a custom context handler keeps track of the state of the file history
panel.
Merge branch 'Feature/ContextHandler' of github.com:rahul-ramadas/sublimetext-filehistory into Feature/ContextHandler

Conflicts:
	file_history.py