Internal key objects should be linked to Strategy Code

[guanidene]

Currently, the following objects of the AlgoBullsAPI class are not linked to the Strategy Code:

1. _key__backtesting
2. _key__papertrading
3. _key__realtrading

The first time any method of AlgoBulls API is called, these keys are fetched and cached for the corresponding strategy code. However, if the methods are called again for a different strategy code, instead of using a key corresponding to them, the cached keys are used which results in incorrect execution.

The solution to this problem is simple: Link the cached keys to Strategy Code. Fetch cached keys only if the strategy code matches, else, fetch the key from the server.

[pushpakdagade]

@shubham-das-algobulls check if this is valid else close the issue.

[prithviraj-gotepatil-algobulls]

This code and function verifies that the strategy codes are mapped with their respective keys using a dictionary.

[prithviraj-gotepatil-algobulls]

All of these were completed in this commit:
8621da5