Adds support for :LOGGING: property

[chuck-flowers]

Addresses issue #466 by adding support for the :LOGGING: property to the note/timestamp insertion logic when updating the TODO state of tasks.

I factored out the parsing framework I created for adding date property support to the agenda search. I used this framework to parse the syntax that orgmode describes in its manual for the :LOGGING: property. I then, determined whether to insert a timestamp or note by first checking for the :LOGGING: property on the affected section and then using the property defined in the user's orgmode config.

[chuck-flowers]

I just realized that master has moved forward since I opened the PR. I can rebase this onto master unless that will cause a problem

[chuck-flowers]

I've rebased on the latest master since git was reporting that there was a merge conflict

[chuck-flowers]

@kristijanhusak I think I have addressed the requested feedback. Please let me know if I have missed something