Refactor parsing for flexibility in handling bus type and availability

The current data model for AC buses has both an entry for the type of bus (PQ, PV, REF, ISOLATED, or SLACK) in addition to availability (true, false ).
The current parser implements the following fixed logic when parsing buses and components:

• If a bus is ISOLATED in the data, the bus availability is set to false and the bustype is set to ISOLATED. The availability of all components attached to the bus is set to false.
• If a bus is not ISOLATED in the data, but is found to be topologically isolated during the parsing (ie not connected to any other buses), the bus and connected component availability is unchanged, but the bustype is set to ISOLATED

The challenge is that real world datasets might require different interpretation on a case-by-case basis (e.g. the meaning of an isolated bus varies). To account for this, the parsing needs to be made more flexible and some of these assumptions should be made configurable by the user.