Reorganize menu classes - categorize them by page modules

Currently Page::Menu::Side represents the side menu for mainly the project page. Now that we are adding tests that uses groups side menu, it does not make sense to add the items for groups side menu into Page::Menu::Side since some them have the same name as that from the project's side menu. Also, we need separation of concerns.

Proposal

Move the selectors for the menu items into separate classes categorized by page modules. So will have these:

QA::Page::Project::Menu

QA::Page::Group::Menu

QA::Page::Main::Menu

QA::Page::Admin::Menu

QA::Page::Profile::Menu and so on.

cc/ @gl-quality