Move servlet initialization code to overridden init method.

Move servlet initialization code to overridden init method.

This is half of the solution to getting proper error messages
displayed when configuration errors occur. Here's the relevant bug:

https://bugzilla.gnome.org/show_bug.cgi?id=662792

The rest of the solution involves surrounding the init method with a
try/catch block and setting a global variable with the error /
exception. A new async method should be created to retrieve and display
the error message / exception.

* src/main/java/org/glom/web/server/OnlineGlomServiceImpl.java: Move
code from constructor to init method adding exceptions as needed.