Improve LS config handling

[M4LuZ]

Expected Behavior

As per #1080:

• System parameter handling should be modified to use access functions instead of direct access to global array variable $cfg
• Default values for all parameters should be returned if not explicitly set
• (optional) these should be set on-change, not on-access
• (optional) Caching of values should be used
• (optional) related DB functions should be moved to the new solution
• (optional) Namespacing & instantiation of variables may be useful

Current Behavior

• Config is read from DB into global array $cfg.
• All access is directly done on that.
• Missing parameters cause a PHP warning, changed default values are not taken over unless module update is done manually.
• Config names cannot be duplicated as they then cause overwrites

Possible Solution

• Create new class with needed functionality
• replace code for initialisation and writing
• use RegEx to find and replace all read accesses
• Double check if for whatever reason there are writebacks
• Profit

Steps to Reproduce (for bugs)

• Access a new setting that has not been written to the db (yet)
• See warning

Context

This causes warnings to pop up regularly on changes and improvements