webadmin,userportal: Minor UI performance improvements

1. Removed use of String.format in client code

   * For simple string concatenation, use "+" operator directly.
     For more complex concatenation, use StringBuilder or Messages.
     StringBuilder and StringBuffer are compiled to browser-specific
     implementation and therefore should be relatively fast.

   * Fixed inappropriate use of patterns (e.g. "test %1$s") in GWT
     Constants interfaces. Constants should be used for constant
     values only. If the values need to be parametrized, use Messages.

   * Interestingly, String.format was heavily used for very simple
     concatenations in CommonModel search string handling.

2. Force reload UserPortal on logout (IE8 or below)

   * For sluggish browsers, it's better to reload entire application
     on logout. UserPortal is intended to be used by common users
     who might have reduced privileges with regard to installing
     alternative browsers. Because of this, force reload on logout
     is implemented for UserPortal only.

Change-Id: I264952895c33454e925ca2c109dd019a61aab879
Signed-off-by: Vojtech Szocs <vszocs@redhat.com>