Corrected structure of ThanksLog table
Refactored ThankfulPeoplePlugin::IsThankable() method
Made field ThanksLog::InsertUserID "nullable"
Added SQL for v_TP_ThanksLog view
Fixed query for ThanksLogModel::GetThanksCountByObjectID() method

* Field "ThankID" was incorrectly declared as ThanksLogID.
* Redesigned main plugin functions:
	* Replaced "ThankFor" method with "GiveThanks" method.
	* Replaced GET commands with POSTed forms.
	* Removed "UnthankFor" (to be replaced with an equivalent method).
	* Updated README.