#280 Avoid usage of resource (rcc) files for icons

[Carlos Pascual]

Building rcc files for icons during taurus setup is an old source of issues, e.g.:

• rcc utility (which is part of qt-devel) needs to be installed at build time. This is specially problematic on win systems
• taurus packages get fatter because of shipping both the rcc and the icon
• setup.py needs to be customised to build the rccs
• It adds an extra step when working directly with sources (calling python setup.py build_resources)
• the .rcc files need to be rebuilt if new icons are added

Tiago once suggested that using the icon files directly instead of via the .rcc files may not have a significant performance hit (if any at all).
Considering that the "taurus-way" of using icons/pixmaps is via the get{Theme}{Icon,Pixmap} functions from the taurus.qt.qtgui.resource module, we just need to refactor these methods in order to implement this change.

Also note that with the drop of support for PyQt<4.8 in taurus4, there is no need to support the case in which qt does not provide theme icons. This also helps in the refactoring.

Once this is done, implementing [#272] (use of xstatic for the icon files) or making this part of [TEP13] (plugins support) may be considered. Also, implementing this, facilitates the implementation of [#279]

[Carlos Pascual]

See an implementation of this feature as part of the implementation of [#279] in the setuptools branch of my fork: https://github.com/cpascual/taurus.git

As it is now, the implementation is complete, but the taurus needs to be adapted to avoid throwing icon-related deprecation warnings

[Carlos Pascual]

My proposed implementation was integrated by teresa to the develop branch. The remaining changes (removing deprecation warnings will be handled as a new ticket [#282])