Use encoded string for server name

If string including special character for URL (e.g. /,?,#) or multibyte
character is given as server name, stapler cannot handle it correctly.

This patch provides encoded server name as url string.

And jelly has something wrong so fix it.

Fix for JENKINS-20291
Change relative link to server in plugin configuration page

This patch generates the relative link to server configuration page from
plugin configuration page.
Structured section of gerrit server config

New div block wraps exisitng the section of gerrit server in plugin
config.

To prevent that other settings override styles for this block, prefix is
added to class name.
Merge pull request #105 from rinrinne/server-name

Use encoded string for server name