webadmin: Control UI plugin dynamic tab alignment

This patch improves the existing UI plugin API for handling
dynamic tabs.

(1) Function improved: addMainTab

New signature:
    addMainTab(label, historyToken, contentUrl [, options])

Example usage:

    // Tab is left-aligned by default
    addMainTab('Foo Tab', 'foo-tab', 'http://www.foo.com/');

    // Tab is right-aligned via options object
    addMainTab('Foo Tab', 'foo-tab', 'http://www.foo.com/', {
        alignRight: true
    });

(2) Function improved: addSubTab

New signature:
    addSubTab(entityTypeName, label, historyToken, contentUrl
        [, options])

Example usage:

    // Tab is left-aligned by default
    addSubTab('VirtualMachine',
        'Bar Tab', 'bar-tab', 'http://www.bar.com/');

    // Tab is right-aligned via options object
    addSubTab('VirtualMachine',
        'Bar Tab', 'bar-tab', 'http://www.bar.com/', {
            alignRight: true
        }
    );

Signed-off-by: Spenser Shumaker <sshumake@redhat.com>
Signed-off-by: Vojtech Szocs <vszocs@redhat.com>
Change-Id: Icd6929538fd106d0c54d162dfd21f8946254ce5f