Update CSS only theme and remove FreeMarker template

[semik]

I think it could be better use only CSS version of Keycloak theme. I think it might be more prone to upgrades than .ftl files. But I had to make some sacrifices. Here is my first attempt.

Login page

Updating user info; this page is shown in case IdP does not provide enough information

An internal server (like in situation with incorrect .ftl file which wont happen again with this patch

I removed background image - personally I think it is visually confusing and unnecessary, the pages looks nice and clean to me without it.

I removed copyright notice because I didn't find a way how to define footer with default Keycloak theme. I think it isn't necessary there.

I had to change format of favicon from svg to ico because default Keycloak theme have favicon.ico name hardcoded.

The only problem I see with it now is that I reference file hosted on github instead of locally hosted one. At this moment, I'm unsure how to resolve this problem. Keycloak uses random string in URI, for example /kc/resources/1zyfx/login/czertainly/img/favicon.ico and I'm unsure how to reference it "../img/czertainly_logo.svg" doesn't work.

Please let me know if other parts of this PR are acceptable, I will try to resolve that issue with logo.

[semik]

Instead of using image linked from github.com I learned about possibility place image using CSS. This way login page looks like original login page generated using .ftl.

Updated images:

For possible test updated image for theme: semik75/keycloak-25-theme:0.15 I've tested it with my local instance of CZERTAINLY running in Virtual Appliance.

Closes #5