add --prefer-lowest-stable to update command
split update --prefer-lowest and --prefer-stable
PluginManager refactoring, fixes #3550
Update deps
Persist prefer-lowest in composer.lock
Bullet-proof global composer instantiation
Merge pull request #3450 from nicolas-grekas/prefer-lowest-stable

add --prefer-lowest and --prefer-stable to update command
Fix tests again..
added --no-progress to self-update

closes composer/composer#3555
Merge pull request #3556 from alcohol/add-option-no-progress-to-selfupdate

added --no-progress to self-update