create fileEMDVeloxWithSpectra & update fileEMDVelox's metadata extraction

[ccatherinetan]

updates to the fileEMDVelox class:

• in getMetadata: include everything in metaDataJSON except for keys_to_ignore ('EnergyFilter', 'Vacuum', 'GasInjectionSystems')
  • whereas, previously only useful_keys ('Optics', 'Stage', 'Scan', 'BinaryResult' ) were kept.

creates new class fileEMDVeloxWithSpectra, inheriting from fileEMDVelox

• overrides _find_groups() to include Image and Spectrum Image data in self.list_data

see most updated description here: MolecularFoundry#3