Fix minor bugs

[kaitlynng]

1. Added DateTime JUnit test
2. Edited help message to allow for editing of remark. Closes Allow editpatient command to edit remark with r/ as well? #262
3. Fix predicate to allow for matching with partial strings. Closes [PE-D] findpatient does not work with partially matched strings as documented in UG #248 and [PE-D] Findpatient command does not work #233
4. Fix UI bug in appt tab.
5. Fix addappt bug that stretches to the next day by disallowing it. Closes [PE-D] Duration on schedule #231
6. Change command "listpatient" to "listpatients" and "listappt" to "listappts"
7. (slightly hacky) fix for white text in menu bar. Closes [PE-D] Invisible items in Menu bar tabs #242

[jianhandev]

LGTM