Allow disabling of PACS tools by manually ensuring exclusivity
Summary: Since the corresponding Qt functionality is not available in our version, as described in T28631, I reimplemented the exclusivity of PACS tools myself to allow the user to deselect the currently selected tool by clicking it again. This disables any functions connected to the LMB, but leaves other PACS interactions (e.g. ctrl + RMB) untouched.
Test Plan: Enable PACS like interaction and load any picture, click a selected tool again to deactivate it -> the LMB does nothing, but secondary PACS interactions still work
Maniphest Tasks: T28631
Differential Revision: https://phabricator.mitk.org/D532