Model version numbering + removal of versioning for collections

[ricalessandri]

As agreed on the Martini dev meeting, collection numbering should be removed. Collection files (which can be useful in certain cases) can be kept with _vYYYYMMDD.itp (but probably all the headers of the models contained in the collection should contain the version number).

Only version numbering for the single models should be added, and they should look like the following:

;;;;;; Martini 3 small molecule topology for benzene (BENZ)
;
; Description:
;   Topology with optimized bond lengths.
;
; Reference(s):
;   R Alessandri, et al., Adv. Theory Simul., 2022, DOI: https://doi.org/10.1002/adts.202100391
;   PCT Souza, et al. Nat. Methods, 2021, DOI: https://doi.org/10.1038/s41592-021-01098-3
;
; Category
;       small molecule
;
; Name
;       Benzene
;
; Alias
;       BENZ
;
; Force field
;       martini3001
;
; Version
;       1.0
;

[ricalessandri]

Maybe then I can keep some collections and name them as follows, e.g.:

• martini_v3.0.0_small_molecules_2022RAAdvTheorySimul.itp (the small molecule paper version)
• martini_v3.0.0_small_molecules_2020PCTSNatCommun.itp (PR #30)