clear the filter term text edit box appropriately

clear the text box when the '+' button is pressed or
when the filter attribute is changed.

also changed the frame style to match the card frame style.
refactor cardframe as a parent of a text card frame and a picture card frame

cardframe is now a stacked widget that prefers to show the card picture
only so that the screen can be more space efficient and the card pixel
map can be displayed as a larger size. however if the card pixel map
can not be loaded for some reason, the cardframe class will automatically
switch to the text version of the card.

a menu item was added under the database menu to allow for users to
prefer card text only.