Update to display class and header

Changelog:
- Restructured display.c further.
- Method changes:
-- LcdWriteFirstLine added: call on this to write text onto the whole
first line !DOES NOT SCROLL!
-- LcdClearFirstLine has been added to clear the entire first line.
-- LcdClearLine has been renamed to LcdClearSecondLine. LcdClearLine has
been deprecated.

Note: When having used the whole first line and returning to the
original layout, don't forget to call upon 'LcdClearFirstLine'.