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

...ned-off-by: Brooke Peterson <brooke.peterson@lge.com>

###Issue:
Whenever ".moon-sub-header-text" is used as a nested class in other CSS classes such as ".moon-video-player-channel-info-name" to avoid 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 color or font-size is different then .moon-sub-header-text class.