reduced width of bar by ICON_OFFSET amount of pixels so the status text on the right is no longer going off the edge of the screen

also reduced the ICON_OFFSET definition by 1 pixel to account for new thingmenu font size
fixed bug where the width of application windows was being reduced
by the ICON_OFFSET width by removing the ICON_OFFSET subtraction from
the affected functions. It should only be applied to the functions
that handle the taskbar.
created killclients function to close all windows in a workspace

note: created function by modifying the closeonclick function
made a number of changes to config.h keybindings

- changed Alt-Tab to focus next client instead of switching to the last selected workspace
- swapped keyboard shortcuts for killclients function and "exit/reload dwm" command
- commented out "exit/reload dwm" function prototype, function definition and keybinding
- changed "previous and next tag" keybinding modifier from Control to Alt (MODKEY)
- removed dmenu-quit command and keybinding
- removed workspace rule for Firefox
minor changes: 1. changed launcher icon letters to lowercase 2. removed pcmanfm floating window rule