Fixes #16 and #20 - Better 7Zip error message and >30 MB size limit.
Fixes the menu commands not working. See Issue #12.

Note:

I think it would be a better idea to move the task commands to Tools
Menu as they don't make much sense under settings.
Merge pull request #21 from dufferzafar/master

Fixes #16, #20 and #12.