Remove ANLTR visitors from the code

[asmelko]

Describe the solution you'd like
The current evaluation of conditional assembly expressions rely on ANTLR visitors. It is due to the fact that these expressions are stored as ANTLR ParsingRuleContext pointer.

However, this is not convenient because to preserve the validity of these pointers, we must not destroy ANTLR parser that created the pointers.

This restricts us in the further development of the plugin.

Acceptance criteria

• Design and implement a new architecture for the CA expressions
• Rewrite grammar rule actions to produce new architecture classes rather than ParsingRuleContext pointers
• Refactor the source code that uses these pointers
• Update wiki pages