[Tilesathome] Change proposal in uploaded files

[Celso González]

Hi

Finally i have some time to program changes and i wanted to ask
for opinions to no duplicate my efforts.

-Do no submit empty files in the zip. Just submit a empty file list
named something like empty_foo and the rest of png files we are sending.
This will reduce the size of the uploads and i think its easy to process
that file in low priority

-Use of tar.gz instead of zip. The processing time is faster and uses
less cpu, the diffs in size are not significant

-Do not save all the path in zip files (or tar.gz), we are currently
saving all the path information in the zip and i think its not a good
idea for privaticy reasons.

-- 
Celso González (aka PerroVerd)  GPG key 0x2DA367B7
http://mitago.net