Ignore IDEA files

Added template from
https://github.com/github/gitignore/blob/master/Global/JetBrains.gitigno
re
[FIXED JENKINS-19934] Job create permission for RoleBasedProjectNamingStrategy.
Show warning for required version, because there is no ways to disable Extension point. Usage on such version will end with ClassNotFound exception. Fixed in [JENKINS-23127].
Added "Apply" buttons for configuration pages.
Removed "go to main page" button - useless.
Merge branch 'for-merge' of https://github.com/KostyaSha/role-strategy-plugin

Conflicts:
	.gitignore

Signed-off-by: Oleg Nenashev <o.v.nenashev@gmail.com>