Add "Triple Click" to keymap event values.

Sounds odd when you read it- but there are many different software (including OS's) that use 'click spam' as a distinct input event. I'm not suggesting they need to change the keymap to utilize it at all (i don't need that kind of drama in my life)- just have it there as an available event for binding custom keys.

Examples:

• in the text editor double click selects an entire word, but triple click could select the entire line
• in face mode, double click could select a loop, triple click could select everything connected to that face.
• in the outliner, you might bind double click to select an object and everything below it in the hierarchy. triple click could select everything back up the hierarchy as well.
• etc..