Digit grouping

http://code.google.com/p/speedcrunch/issues/detail?id=58

Add support for digit grouping for all expressions and results.

A space between groups is added. That space is not a character, but rather a
font property. Therefore it is not copied when users copy and paste expressions.
Digits in the fractional and the exponent parts are also grouped.

The size of the groups depends on the radix:
    - 3 digits for decimal and octal
    - 4 digits for binary and hexadecimal

This feature shall be configurable by the user via Settings in a future commit.
Fix digit grouping change: compare with 128, not 256
Add Tey to the credits
[ResultDisplay] Require QPlaintextEdit since Qt 4.6 is required
[Editor] Paint a customized cursor according to a color scheme
Handle zoom and scroll events from within Editor instead of MainWindow

New shortcuts:
   - Scroll up one page:      PageUp
   - Scroll down one page:    Page Down
   - Scroll up one result:    Shift + PageUp
   - Scroll down one result:  Shift + PageDown
   - Increase font size:      Shift + Up
   - Decrease font size:      Shift + Down

The result display does not get focus.
Style all ResultDisplay and Editor visual elements via color scheme
[ResultDisplay] Paint top/bottom fade effect when scroll available
[ResultDisplay] Regenerate overlay gradient bitmaps on color scheme change

This fixes the previous commit.
[ResultDisplay] Animate page scroll
[ResultDisplay] Improve scrolling input responsiveness
[ResultDisplay] Scroll smoothly with wheel events too
Remove the Keypad

SpeedCrunch is keyboard-oriented and not just another standard-looking
calculator. Also, the keypad added significant complexity to the code.

This change also cleans up the style in Settings.
Don't allow hidden menu bar on OSX and Ubuntu
[Evaluator] Code clean-up and style adjustment
[testevaluator] Remove tests about no arguments

Each function now returns a specific usage error string instead of NaN when no
arguments are used.
Add support for comments at the end of expressions

https://code.google.com/p/speedcrunch/issues/detail?id=293

Any text following a '?' (question mark character, inclusive) will be ignored
for evaluation purposes. It is kept visible in the result display and history
and has its own highlighting color.
Give some love to Evaluator code style
[testevaluator] Coding style
[evaluator] Fix wrong evaluation of powers involving unary minus sign in base

https://code.google.com/p/speedcrunch/issues/detail?id=160

This workaround fixes the issue by:
    . prepending a zero to the expression in case it starts with a unary minus
    . replacing occurences of (- with (0-
This way, the minus sign is not unary and the power operation is correctly
evaluated by the current parser. A proper fix in the future is to rewrite the
parser.