collection of improvements

[whizkid79]

• add possibility to have category image overwritten during import using setAllowRenameFiles
• fix for empty smart categories beeing added

collection of fixes from other PRs:

• fix sorting options and defaults in categories
• using enterprise import

[avstudnitz]

Thanks, but sorry: we can't let the module depend on Enterprise_ImportExport.
In any case, I'd prefer seperate pull requests for seperate issues - combining already existing PRs makes it more difficult to merge.

[whizkid79]

i you don't stack the PR so high, we don't need to combine them to get a working version.
Looks like you do a bit of cleanup. let me know, when you are done, i can separate the different topics.

the issue with depend on Enterprise needs some solution thou, maybe a mockup for CE to fall back on the CE modules...