feat: findMetSmiles and improved DLKcat I/O

[edkerk]

Main improvements in this PR:

As suggested in #171

• feat:
  • findMetSmiles function for querying PubChem for SMILES using metabolite names.
  • DLKcat in- and output files have reaction and gene IDs, to prevent the use of DLKcatIDs structure.

I hereby confirm that I have:

• [x] Tested my code with all requirements for running GECKO
• [x] Selected devel3 as a target branch (top left drop-down menu)

[feiranl]

Please also output the rxnID in the DLKcat input file, so it would be much easier for later mapping.

[edkerk]

The changes in this PR does that (see line 80 in the new writeDLKcatInput and line 47 in readDLKcatInput)! If you approve this PR it can be merged to devel3