More flexible command handling

Multiple changes:

• Allow not having a [parallel] section
• Remove the parallel boolean in general
• Rename ArgvProfile to StandardProfile since this name seems more communicative, covering many cases
• Remove .name attribute on StandardProfile
• Enable "extended" interpolation in configparser so we can do thing = ${otherthing}
• Profile classes have only self.command now, not binary. For non-production runs or other purposes one would create profiles with different commands. We should try to consolidate BaseProfile and StandardProfile wholly or partially in the future.
• Add "configvars" attributes to profiles which is a way to specify statically what strings are expected. This means e.g. Siesta can have pseudopotential paths and DFTB can have skt_path.
• Remove the old boolean from Onetep which apparently doesn't do anything that we cannot do by preprocessing the command
• Add configurable parameters for pseudopotentials etc. where appropriate

Closes #1468 (closed), #1392 (closed), #1292 (closed).

Checklist

• I am familiar with ASE's contribution guidelines.
• Doc strings in code changed in this MR are up to date.
• Unit tests have been added for new or changed code.
• Issue is resolved via "closes #XXXX" if applicable.