[entropy.tools] drop stale comments
[entropy.client.interfaces.package] drop type checking
[entropy.client.package] fix config protect and mask handling

We must collect the configuration protection and masking bits before
the installed package metadata goes away. This is true for both
install and removal paths.
[entropy.client.package] some cleanups
[entropy.client.package] rewrite config_protect+mask handling code

Improve code quality, remove several redundant parts, use set()
objects instead of list() for both protect and mask data.
Improve speed, save the world.
[entropy.const] drop all the config_protect+mask objects from etpConst
[entropy.client.package] make _handle_config_protect() faster, use sets