Make a CSS rule for all text boxen
Add formatting for parameters of type "int" in ValueCell

Note that IntegerBox doesn't provide scientific notation.
Add formatting for parameters of type "float" in a ValueCell
Combine event handlers for "int" and "float" types in ValueCell
Remove "parameter" parameter for ValueCell#isInRange
Remove "parameter" parameter from ValueCell#isParameterTypeNumeric
Check for out-of-range parameter value when defining ValueCell

This fixes #32.