Support for dates and other timestamps

[TheDuckCow]

I am logging this as I am intending to develop it myself and submit a pull request. The idea: provide yet another format in addition to "number" and "time", and call it "date" (or, to expand the options of "time" and allow to have date as well".

Supported formats:

• 01/23/45
• 01/23/2045
• January 23, 2045
• {language lookup??} 23, 2045
• By text formatting. e.g. allow user to input to text field "{y_full}-{m_num}-{d}" to get "2045-01-23"

Additionally, for both time and for date formats:

Create an operator which provides a popup for entering the values at a point in time with more natural fields. E.g. being able to explicitly write in the minute box, hour box, day box etc. On pressing OK in this operator, it translates these values to the correct number in the field (and if auto-key is on and the field was previously keyframed, insert a new / overwriting keyframe).