MassBalance and EnergyBalance needs to be generalized.

[At11011]

In blocks.rs, we need to generalize the approach to track all streams entering and leaving the block for mass and energy balances. The following can be done:

• Track all connectors, not just a single mass in-mass out value pairs
• Compare relative error, for example, the total difference as compared to the total input. This should be an adjustable parameter similar to TOLERANCE_ENERGY and TOLERANCE_MASS, but should be dimensionless instead.
• The mass_balance_check function should just take a &self reference, instead of actual value arguments. The blocks should contain references to Mconnectors and Econnectors (these I also believe should be revised, but that is a later issue).

I have included TODO's in the style-fix branch (to be uploaded in due time) that reference this issue.