Fix memory issue and add functionality to python interface

[menon-karthik]

Current situation

Closes #92 and #82.

Release Notes

• Fixed the issue described in Memory issue in the python interface #92 by changing the model object in Solver to a pointer.
• The issue with Interface doesn't function as expected when using steady initial condition #82 was that the steady state model used for the initial condition was not being converted back to unsteady.
• Added new functions to the python interface to read and update block parameters from python.
• Minor updates to the documentation and error handling.

Testing

Tests are passing. I haven't added new tests for update_block_params and read_block_params in the python interface. Need to think about how to test that within the current testing framework.

Code of Conduct & Contributing Guidelines

• I agree to follow the Code of Conduct and Contributing Guidelines.

[menon-karthik]

Update: I broke something by trying to rebase with master after all the name changes. So this is not ready yet.

[menon-karthik]

Ready now!

[mrp089]

Looks good, @menon-karthik! Thank you for adding more documentation and error handling on the go!