User-specified minimum species per phase overridden when system has 2 or fewer elements

[maxposchmann]

Describe the bug
When the number of elements in the system is 1 or 2, the minimum number of species per phase is set to 1 instead of the normal default of 2. This is in CheckSystem.

The problem is that the way this is implemented prevents users from setting a custom value for minimum species per phase, for example the quite reasonable choice of leaving it at 2 with 2 elements in the system.

Suggestion
This section should be rewritten to check if a minimum species per phase was input by the user (i.e. in an input file). This will require some modification of the input file parsers and the part of CheckSystem linked above.
There will likely need to be a logical flag for this, and users writing .F90 drivers would need to set that flag manually.

Expected behavior
These changes should only affect calculations where a user set the minimum number of species!