Add parameterized mixin class for .moon-sub-header-text Enyo-DCO-1.1-Sig...

### Issue:
Whenever "`.moon-sub-header-text`" is used as a nested class in other CSS classes such as "`.moon-video-player-channel-info-name`", there was double declaration on font color property.

### Fix:
Create a "`.moon-sub-header-text-base`" to take two parameters font-size and font-color so this can be used as a nested rule in case of font color or font-size is different than `.moon-sub-header-text` class.