Add Control-Shift-C hotkey to copy selected task to task edit field

Adds a feature to quickly copy existing tasks to the task edit field via
Control-Shift-C.
Closes (bug) #184: Misinterprets task description as a Project

Changed regular expression for project pattern in the Task class to
require either a space or beginning of line before the plus sign. The
space is not retained in the regex match.

Closes bug #184: Misinterprets task description as a Project (bug).
Merge pull request #185 from mjdescy/dev

Add Control-Shift-C hotkey to copy selected task to task edit field
Preparing release 2.3.1