Show question search results, filter privacy

Closes #11, fixes #4 and fixes #18
Results are output in #qContainer .question using a modified version of
printQ()
Exact username should be provided at From / To user
Found questions must belong to a user that lets the current user see
them.
Various small improvements

Background is fixed
Check username for ^\w{5,20}$ at register
Add lang="en" and meta application-name at index
Autofocus at textarea and echo <time> at printDate() at answer