utils: increase/decrease font size with Ctrl+{+,-,0}

resources/misc/projectcredits.html

src/app/appsettingsmanager.h

src/app/commoncomponents/TextMessageDelegate.qml

src/app/constant/JamiStrings.qml

src/app/constant/JamiTheme.qml

src/app/mainview/MainView.qml

src/app/mainview/components/KeyboardShortcutTable.qml

src/app/settingsview/components/DeviceItemDelegate.qml

src/app/settingsview/components/MediaCodecDelegate.qml

src/app/settingsview/components/SystemSettings.qml

src/app/utilsadapter.cpp

src/app/utilsadapter.h