Support Z in tag date

[slamdev]

Some tags have Z in the end of the date string that breaks the deletion by date feature.

PS: not a python dev, not sure if that can be done better

[hcguersoy]

@slamdev Thank you contributing. I'll check and merge as soon as I've some spare time.

[hcguersoy]

Looks good.
Even I've not seen yet images this such kind of creation date with the Zulu-Time marker (but some blogs reporting this), IMO all Z should be wiped out. At any place.