Add EffectiveTime, RouteCode, and DoseQuantity

Add the following classes:
1. EffectiveTime - General purpose for time elements. Has the ability to
write xml.
2. RouteCode - How medications are taken
3. DoseQuantity - Dose information. Gave it ability to detect if input
has value and unit combined so that it can parse them out. Some
databases use this as one field, but the CCD spec splits it out.
TODO: Need to make design choice if I want all classes to have the
ability to accept an xpath for writing their own elements or if that
should be abstracted out. Currently, I give general Entry classes the
ability to use an xpath for writing, but I decided here that I didn't
want to allow my more specific Medications classes to have this ability
as the actual writing of xml is done in the class that extends
SectionList.