Add resources to Developer Guide

[Gnafu]

Adds instruction on own to customize the Theme and the search box services
Also make the standalone demo page accessible again

[coveralls]

Coverage remained the same at 79.863% when pulling 847ec98 on Gnafu:user_guide1 into 39a44f3 on geosolutions-it:master.

[mbarto]

This does not seem a user guide to me

[offtherailz]

Yes it looks more like a work in progress. Should we place some "TODO" here and there to make it become a user guide?

[coveralls]

Changes Unknown when pulling b53104a on Gnafu:user_guide1 into ** on geosolutions-it:master**.

[mbarto]

Maybe we should simply remove what is not interesting to users, or redefine what a user is: a developer, a configurer, a designer (themes) or someone who uses the application?
This is not clear to me. From this PR it can be one of the first 3 roles, but not the last one.

[coveralls]

Changes Unknown when pulling b53104a on Gnafu:user_guide1 into ** on geosolutions-it:master**.

[Gnafu]

Whatever solution is fine for me, I just don't want to loose this informations as they are not documented anywhere (or they are buried in the mapstore-users mailing list)

[mbarto]

I was wondering if the stuff you wrote is more developer oriented, than user oriented, and we already have a developer guide (where you can add new pages, if you like)

[coveralls]

Coverage remained the same at 79.895% when pulling 33b46ab on Gnafu:user_guide1 into 4014813 on geosolutions-it:master.

[Gnafu]

Moved them to the developers guide

[coveralls]

Changes Unknown when pulling 28b02e2 on Gnafu:user_guide1 into ** on geosolutions-it:master**.

[offtherailz]

Sorry if I take this too late, but the theme customization is for the dev guide, but the search services configuration is accessible from the web, so it's part user's guide, in my opinion. Should we merge this anyway?