WIP: Version 2.0.0 next major release

[sjoerdtalsma]

Changes intended for v2:

• Minimum Java version to 1.8
• Remove relocation modules
• New base package to avoid conflicts with v1
• Remove deprecation
• Replace getActiveContext by getActiveContextValue (and return Optional value)
• Create a 'bridge' to v1 ContextManager implementations (including v1 values in v2 snapshots too)
• Refactor built-in context managers to public Context with inner Manager class implementation
• Proper jigsaw module info (Add jigsaw module information to this library. #1)
• Resolve Javadoc 11 / maven-javadoc-plugin issues (Bump maven-javadoc-plugin from 3.0.1 to 3.1.0 #108)

[sjoerdtalsma]

Closing the pull request for now as I currently don't seem to have the cycles to spend to do this properly; perhaps I can revisit some later time