[FEATURE] Fallback/default case for SwitchViewhelper

In order to provide the full functionality known from the
switch/case PHP function, a default case possibility is
introduced. Use it like:
<f:switch expression="{person.gender}">
  <f:case value="female">Mrs.</f:case>
  <f:case value="male">Mr.</f:case>
  <f:case default="TRUE">Mrs. or Mr.</f:case>
</f:switch>

Change-Id: Ib9468cdabd66fb8b484cb4d07520d5b529548dd1
Resolves: #49371
Documentation: #54283
Releases: 6.2
Reviewed-on: https://review.typo3.org/26058
Reviewed-by: Benjamin Kott
Tested-by: Benjamin Kott
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring