Add Exercise: Trigonometry 2.5: Finding Missing Sides with Basic Trig Ratios

New trigonometry exercise, based upon the existing trigonometry_1.5 exercise.  The exercise has the user solve for one side of a right triangle, given the length of a second side and one angle in degrees.

This exercise is based upon the spec in Trello card #502: https://trello.com/c/df95ci9b

The hints are based upon the trigonometry_1.5 exercise instead of the spec on the Trello card, as I thought the existing hints from the trigonometry1.5 exercise made more sense.