Add Core::Elements::atomicNumberFromName lookup function.

Also improve documentation and error return values.

Change-Id: If7b08a2b698ba039cc1fad66d4f0ed448c54441a
Pull out a CoordinateBlockGenerator from InputGenerator.

There is a very flexible coordinate block generation routine in
the InputGenerator class. Move this into its own class and port
to STL.

Change-Id: I5dd7d6719cf0462dc1ec7cb53d126a79b6bf66fd
Add a free-text cartesian coordinate editor.

Change-Id: I3ac1f581ae72aec711f065bf935075848e3677f7
Merge remote-tracking branch 'origin/master' into cartesian-editor

Conflicts:
	avogadro/qtplugins/CMakeLists.txt

Change-Id: Ia370c887c0436dc9c45bf477897b5c6dd8c08eae
Merge topic 'cartesian-editor' into master

2009a32d Merge remote-tracking branch 'origin/master' into cartesian-editor
0305dba5 Add a free-text cartesian coordinate editor.
562305fd Pull out a CoordinateBlockGenerator from InputGenerator.
c22bd9a3 Add Core::Elements::atomicNumberFromName lookup function.