Enable modifications of rules

[NDietrich]

This is a major feature that's needed.
After all rules are downloaded, PP needs to have a mechanism for the rules to be modified based on user needs (changing 'alert' to 'drop' when the severity > 2 for a simple example).
This can be done with a DSL (domain specific language) and the Lark parser. Basically we create a grammar describing an individual rule, and have Lark parse each rule into a parse tree.
we then have a DSL that allows the user to write complex rules that will modify the ruleset rules. Some DSL rule examples:

disable ((gid != 1) and (metadata contains "community"))
modify (action = reject ) where (sid > 1000)
modify (dst_ports = 'https_ports' ) where ((dst_ports == "https_ports")   and (flow != "to_client" ) )

The user would create a file with these commands in them, and PP would use these DSL rules to modify the rules individually.

I have code that does this, but it's not ready for primetime yet (slow when it scales up, and there are a few edge cases in the grammar describing a rule which I need to handle.
I'll create a new branch for this feature so people can test it once I iron out a few bugs.