discriminate frames with virials labels in Multisystem class

[PKUfjh]

Sometimes we came across with multisystem (such as quip/gap/xyz format files) which has both frames with virials labels and frames without virials labels. The current implementation of the Multisystems class will lead to error message:

RuntimeError: system has virial, but this does not

But this kind of Multisystems are in fact trainable, so I identify frames with virials in Multisystems, such that Systems will have names as:

C60  C60_virials

The former represents systems with 60 carbon atoms without virials labels, the latter represents systems with 60 carbon atoms with virials labels.

[codecov-commenter]

Codecov Report

Merging #294 (31438f0) into devel (c0bb798) will decrease coverage by 0.03%. The diff coverage is 40.00%.

@@            Coverage Diff             @@
##            devel     #294      +/-   ##
==========================================
- Coverage   81.57%   81.53%   -0.04%     
==========================================
  Files          62       62              
  Lines        5244     5249       +5     
==========================================
+ Hits         4278     4280       +2     
- Misses        966      969       +3     

Impacted Files	Coverage Δ
dpdata/plugins/ase.py	64.51% <0.00%> (-3.29%)	:arrow_down:
dpdata/system.py	85.28% <100.00%> (+0.04%)	:arrow_up:

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[PKUfjh]

This is a breaking change to the code that has potential influence on other codes using dpdata.MultiSystems with explicit formula.

I do not support the merging of this PR.

Actually this change just modifies the system names in the MultiSystems frames (add "_virials" to the system names), I do not see what negative influence this change will have on other codes.