Allow dynamic dates based on a pattern

The Issue

The current way to display time on a hologram is very limited.

Justification for this PR:

Allow more more customization of holograms, providing a more "all in one" package. 

PR Breakdown

Adds a new tag that can be specified on hologram creation.
The tag is: %date:'date format'%
The 'date format' part will be phrased by java's SimpleDateFormat then the whole tag is replaced by the output.
The syntax can be found here: http://docs.oracle.com/javase/7/docs/api/java/text/SimpleDateFormat.html

 eg: The time is: %date:"h:mm a"% will be The time is: 12:08 PM

Relevant PR(s) and Issue(s)

Currently it's pointless to display any unit below minutes.
Since holograms are only refreshed every 1 minute.