Minor time format bugfix

When setting the time format under the "cfg regn"/"time fmt" menu, all
settings should revert back to their previous values if the user
presses the "menu" button to exit the menu.  But the colon style would
remain changed if the user exited the "dst show/hide" menu or
"gps show/hide" menu.  This has been fixed.
Minor code clarity edits

Updated comments in icetube.c  Also, clock speed is now set to 2 MHz
on startup to save a bit of power during an initial sleep.