Added atomCount with atomic number, and mass

Simple implementation to get the atom count for any given element,
molecular mass calculation. Simple testing added for both.

Change-Id: I86a1453faaa3b6ed11cdf05ff48cd847c06e95b9
Merge 'origin/master' into molecule-enhancements

Conflicts:
	tests/qtgui/moleculetest.cpp

Change-Id: I27ee583e4cf9c26057906f9db8c402d58706d360
Merge topic 'molecule-enhancements' into master

af966739 Merge 'origin/master' into molecule-enhancements
5d717f57 Added atomCount with atomic number, and mass