GODT-1554 / 1555: Implement gRPC go service and Qt 5 frontend C++ app.

WIP: updates

WIP: cache on disk and autostart.

WIP: mail, keychain and more.

WIP: updated grpc version in go mod file.

WIP: user list.

WIP: RPC service placeholder

WIP: test C++ RPC client skeleton.

Other: missing license script update.

WIP: use Qt test framework.

WIP: test for app and login calls.

WIP: test for update & cache on disk calls.

WIP: tests for mail settings calls.

WIP: all client tests.

WIP: linter fixes.

WIP: fix missing license link.

WIP: update dependency_license script for gRPC and protobuf.

WIP: removed unused file.

WIP: app & login event streaming tests.

WIP: update event stream tests.

WIP: completed event streaming tests.

GODT-1554: qt C++ frontend skeleton.

WIP: C++ backend declaration.

wip: started drafting user model.

WIP: users. not functional.

WIP: invokable methods

WIP: Exception class + backend 'injection' into QML.

WIP: switch to VCPKG to ease multi-arch compilation,  C++ RPC client skeleton.

WIP: Renaming and reorganisation

WIP:introduced new 'grpc' go frontend.

WIP: Worker & Oveerseer for thread management.

WIP: added log to C++ app.

WIP: event stream architecture on Go side.

WIP: event parsing and streamer stopping.

WIP: Moved grpc to frontend subfolder + use vcpkg for gRPC and protobuf.

WIP: windows building ok

WIP: wired a few messages

WIP: more wiring.

WIP: Fixed imports after rebase on top of devel.

WIP: wired some bool and string properties.

WIP: more properties.

WIP: wired cache on disk stuff

WIP: connect event watcher.

WIP: login

WIP: fix showSplashScreen

WIP: Wired login calls.

WIP: user list.

WIP: Refactored main().

WIP: User retrieval .

WIP: no shared pointer in user model.

WIP: fixed user count.

WIP: cached goos.

WIP: Wired autostart

WIP: beta channel toggle wired.

WIP: User removal

WIP: wired theme

WIP: implemented configure apple mail.

WIP: split mode.

WIP: fixed user updates.

WIP: fixed Quit from tray icon

WIP: wired CurrentEmailClient

WIP: wired UseSSLForSMTP

WIP: wired change ports .

WIP: wired DoH. .

WIP: wired keychain calls.

WIP: wired autoupdate option.

WIP: QML Backend clean-up.

WIP: cleanup.

WIP: moved user related files in subfolder. .

WIP: User are managed using smart pointers.

WIP: cleanup.

WIP: more cleanup.

WIP: mail events forwarding

WIP: code inspection tweaks from CLion.

WIP: moved QML, cleanup, and missing copyright notices.

WIP: Backend is not QMLBackend.

Other: fixed issues reported by Leander. [skip ci]

go.sum

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