Details:  more consistent with the File menu

Many singletons have their own instance() method, in which case there is
no need to use ICore::instance() to get access to them.

replace ExtensionSystem::PluginManager::instance()->getObject<Core::ICore>() by Core::ICore::instance()

forward declaration is sufficient.

Details:  - Naming convention

Details:  - Conform to naming convention

Details: Refactor the git command to be able to run a batch. Run diff and diff --cached in a batch

Details:  - To make it conform to naming convention.

Fixes: Random enabling of submit/diff buttons when switching contexts (viewing diffs) from the submit editor

Details: Register actions directly

Fixes: Make git diff work for staged files, do not launch submit if file list empty, make file  model read only, add conveniences

Details: Add a type data field to the git file model

Task: 205821
RevBy: con
Details:  Add a IVersionControl to git. Extend IF to able to return a name and add enabling options. Connect project explorer to enable the right VCS.

Task:     -
RevBy:    -
AutoTest: -
Details:  -