Convert fixhdr to py3

Codes have been converted to py3 and tested with miniseed sample downloaded from IRIS webservices. Need more testing from someones who are used to fixhdr.

Fix bug in tab Endianess when 'Convert to Little', error happen when unpack inblk to variables with time (Year, Day, Hour, Min, Sec, junk, Micro) in Mseed.Writeblk200/201/300/310/320/390/395/500.

Fix bug in tab Time Shift when 'Recalc Start/End' with no 'Stat:Loc:Net' in MainWindow.GetStartEnd()

There is a bug in PmwColor.bordercolors of python 3's site-packages that lightRGB and darkValue's items need to be converted to integer. Derick said he had a batch for this. So, consider apply the batch before running this fixhdr version in python 3

changed the description

assigned to @dhess

mentioned in commit 123ca036

merged