Refactor UI control drawing to add styles and reduce the number of parameters

[DaleStan]

This is my proposal for improving the too-many-parameters problem brought up in #220 (comment). It combines parameters that routinely appear together, provides easy access to common combinations, and eliminates most situations where a caller can't pass all the appropriate options.

The intentional user-visible changes are:

• Refuse to accept negative numbers for things like fixed and built building count.
• Reduce the leading padding from 0.8 to 0.5 in all text input boxes that didn't already use 0.5. (Except the 'create directory' text box in the filesystem window, which still uses 0.2 x 0.2.)
• Change the MilestoneDisplay.Normal icons in the NEIE to Contained instead. (see ImmediateWidget.cs:12-24)

[shpaass]

This is awesome!