setup.py build_ui incorrectly checks file dates

In setup.py, the build_ui code checks for the respective dates for the x.ui and ui_x.py files to determine whether it should recompile. Unfortunately Git updates the timestamp of files every time it changes a file during a Checkout - so this is not a great way of deciding whether a recompile is necessary.

Perhaps it would be better to recompile to a temp file, then compare the files (ignoring differences in the opening comments such as file path (which could have / or ) the compile date and pyqt version) and see if the code is different - and if it is copy the code over to the picard/ui directory to replace existing.