Add diag flag to help manual and update manual metadata (#707070)

Part of Bug #707070 - Update Help Manual with GPT flags, Force Cancel
                      button, etc.
Add list of gpt flags to help manual (#707070)

Part of Bug #707070 - Update Help Manual with GPT flags, Force Cancel
                      button, etc.
Add changes for Force Cancel button to help manual (#707070)

A "Force Cancel" button and proper cancel support was added to
GParted 0.15.0 with the following commit:

  Add proper cancel support (#601239)
  89de9a50269c2f92208a549f0e5feb6127ca7d30

Part of Bug #707070 - Update Help Manual with GPT flags, Force Cancel
                      button, etc.