fixed division by zero and few other bugs and enchanced whos online and staff online modules

Fixes for whos online and staff online modules.

- fixed division by zero bug and various other bugs within these 2
modules.
- added functionality where value of 0 for columns or rows set in
options panel will hide avatars and leave only text output.
- added text output to staff online module in case of disabling avatars.
- changed various language variables for these 2 modules.
- improved tip for modules in options panel
fix invalid html rc2
1.3.4 release to address Issue #16 Issue #14 Issue #9 and Issue #17

Issue #16

Added seamless upgrade module thanks to help and code from pavemen and his MyBB Publisher plugin. Version control is now possible using the cache and upgrade instructions will now be consistent for all versions:

Deactivate plugin
Overwrite files
Activate plugin

Issue #14

Removed on-the-fly custom box type as it has been deprecated by group decision.

Issue #9

Added independent setting for latest_threads module as suggested.

Issue #17

An attempt to clear up an error with headers being sent erroneously causing an irritating error.