Change menu Item "Slide->Master Slide" to "Slide->Change Slide Master"
Change dialog name "Slide Design" to "Available Master Slides"
Change dialog name "Load Slide Design" to "Load Master Slide"

Change-Id: I98fab31cdce2e8ddf43f0c8b8519a95e15c13de5
Reviewed-on: https://gerrit.libreoffice.org/65860Reviewed-by: Heiko Tietze <tietze.heiko@gmail.com>
Tested-by: Heiko Tietze <tietze.heiko@gmail.com>