Create stable version of I2C core

[hiddemoll]

The I2C core moved from the examples to Clash-Cores as an Experimental module. There are a few things which we want to do before promoting it from its experimental state.

TODO

• Expose debug flag of both I2C unittest subcomponents (Config.hs, Slave.hs)
• Add tests for smaller portions of the I2C core
• Refactor code to be more uniform
• Replace master/slave by controller/target
• Move files from Experimental subdir