Move capa templates into the capa library

common/lib/capa/templates/choicegroup.html

common/lib/capa/templates/imageinput.html

common/lib/capa/templates/jstextline.html

common/lib/capa/templates/mathstring.html

common/lib/capa/templates/schematicinput.html

common/lib/capa/templates/solutionspan.html

common/lib/capa/templates/textinput.html