ISSUE-208 better accessibility, no idp is selected if the input is empty and fix layout.

...pp/src/main/java/edu/kit/scc/webreg/bean/HeadBarBean.java

...ava/edu/kit/scc/webreg/bean/disco/DiscoveryLoginBean.java

...sources/META-INF/resources/primefaces-kit-theme/theme.css

bwreg-webapp/src/main/webapp/resources/css/std-ext.css

bwreg-webapp/src/main/webapp/template/head-bar.xhtml

bwreg-webapp/src/main/webapp/user/connect-account.xhtml

bwreg-webapp/src/main/webapp/welcome/index.xhtml