bundle-ng: move bundle generation to changegroup.py

bundle-ng: unify _changegroup and _changegroupsubset Refactor the two changegroup generation interface to share as much code as possible.

bundle-ng: move gengroup into bundler, pass repo object to bundler No semantic changes made.

bundle-ng: add bundlecaps argument to getbundle() command

bundle-ng: move group into the bundler No additional semantic changes made.

bundle-ng: move bundler creation up in the stack Create a simple start() method to pass the lookup function until bundler becomes smarter and gets a repo object. Since we now create the bundler for the whole lifetime, we need to pass it down to revlog methods.

i18n: fix untranslated prompts with translated responses (issue3936)