Implementing workchains

[ezpzbz]

Currently, only simple calculations are added to the plugin. As ORCA calculations are complex and in real-world usage one would combine several steps of optimization, frequency calculation and so on, I should implement few workchains to cover basic protocols of calculations.
[UPDATE]
I am working on having following workchains for the next release:

• OrcaRelaxationWorkChain: It should take structure and optimizes the geometry with basic error-handling. On demand, it should be able to run consequent frequency calculation to verify if the relaxed structure is local minima or transition state.
• OrcaEmissionSpectraWorkChain: It shoudl take structure, relaxe it, and perform ASA calculation to give us the emission spectra.