frontend: generate module components from a separate checkboxes
    
    Fix RHBZ 1832395
    
    When the module generation form was initially implemented, I
    misunderstood the meaning of the `filter` field and mistakenly tied
    `filter.rpms` and `components.rpms` together. That is not how it is
    supposed to work.
    
    According to the official documentation `filter.rpms` is:
    
        # RPM names not to be included in the module.
        # By default, all built binary RPMs are included.  In the example
        # we exclude a subpackage of bar, bar-nonfoo from our module.
        # Defaults to an empty list.
        #
        # Type: OPTIONAL
        rpms:
    	- baz-nonfoo
    
    According to the official documentation `components.rpms` is:
    
        # RPM content of the module
        # Keys are the VCS/SRPM names, values dictionaries holding
        # additional information.
    
    Therefore I am changig our current `filter` field to not render all
    checkboxes selected by default (i.e. nothing is filtered out of the
    module by default). And I am adding a new box with checkboxes named
    Components, that will allow you to select unique SRPM package
    names. The resulting module will contain `components.rpms` solely from
    this field.
    
    Ideally, we would like to have some smart Javascript thingy to show
    items in Package Filter, Module API, and Install Profiles boxes that
    are provided by the currently selected Components SRPM packages and
    hide the rest of them. This would help us solve the biggest drawback
    of the module generation form - it being too long for projects with
    many packages.