Streamline stackbuilder by getting rid of login credentials

[robe]

As Paul noted having the super user credential prompt in stack uilder is only useful for the "Create spatial database" and frankly installer shouldn't be doing that. So we should get rid of it in the installer.

​http://lists.osgeo.org/pipermail/postgis-devel/2014-January/024068.html

Now that we have CREATE EXTENSION we should just have people do that. Might e useful as a final dialog or something to note the various create extension options:

Because creating the sample database installs

CREATE EXTENSION postgis;
CREATE EXTENSION postgis_topology;
CREATE EXTENSION postgis_tiger_geocoder;
CREATE EXTENSION pgrouting;

and for 2.2 we'll be including point cloud as well. Would be useful for people to be aware of all these packaged extensions in some easy way.

[robe]

I decided to keep the create spatial database option. Seems people actually find that useful especially if you are creating a silent installer (which I gotta fix).

However, I did change in 2.1.3 release so that if the create spatial database option is not checked, then the username/password dialog screen will not come up. By default it isn't checked. It will come up if create spatial database option is checked.