Move configuration of the servlet to the constructor.

Move configuration of the servlet to the constructor.

The servlet will be initialized even if the database authentication
information is not set or correct. I still need to add the UI for prompting
the user for the authentication information when it's required.

* src/main/java/org/glom/web/client/OnlineGlomService.java: Add
javadocs for getDocumentTitles() method.
* src/main/java/org/glom/web/client/activity/DocumentSelectionActivity.java:
Set error message when RPC fails.
* src/main/java/org/glom/web/server/OnlineGlomServiceImpl.java: Get the
glom files directory from the configuration file. Try to set the
database authentication information for the specific document if it's
set and works otherwise try to use the global authentication
information set for the directory.
* src/main/resources/onlineglom.properties: Moved from
src/main/webapp/WEB-INF/OnlineGlom.properties. Updated with new keys.
Added detailed comments for the new keys.