Review: adding lower-level objective gap and pessimistic case related functions

[yuxies]

The main changes in this draft:

• add gaps to related functions in UB problems setup and cut generations;
• add pessimistic related parameters and variables; add containers and tags to the linking solution pool; (these changes introduced check failure on call stack...)
• in MibSBilevel, change the feasibility checking procedures and add related problem setup functions;
• in MibSModel, add a function to store coefficient matrices A1, A2, G1, and G1 since they are used in pessimistic problem setup functions;
• in MibSCutGenerator, remove getLowerMatrices() as it is replaced by the function above; related lines that appeared in finding solutions for the (watermelon) intersection cuts are also removed;

A segmentation fault was introduced after adding the pessimistic parameters. Still trying to figure out where it was caused...

Will have more updates after running tests.