Display code update

[LeeLeahy2]

This change includes:

• Moves all display code into Display.ino
• Moves all display variables into Display.ino
• Eliminates duplicate code
• Common code to handle icon blinking
• Use bit vector to determine which icons to display

[nseidle]

This is a big contribution - Thanks @LeeLeahy2! Works well on the Facet/Express/Surveyor.