misc: move JamiTheme and JamiStrings to net.jami.Constants namespace

src/MainApplicationWindow.qml

src/commoncomponents/AccountMigrationDialog.qml

src/commoncomponents/AvatarImage.qml

src/commoncomponents/BaseContextMenu.qml

src/commoncomponents/BaseDialog.qml

src/commoncomponents/DeleteAccountDialog.qml

src/commoncomponents/ElidedTextLabel.qml

src/commoncomponents/GeneralMenuItem.qml

src/commoncomponents/GeneralMenuSeparator.qml

src/commoncomponents/InfoLineEdit.qml

src/commoncomponents/JamiFileDialog.qml

src/commoncomponents/ListViewJami.qml

src/commoncomponents/LookupStatusLabel.qml

src/commoncomponents/MaterialButton.qml

src/commoncomponents/MaterialLineEdit.qml

src/commoncomponents/ModalPopup.qml

src/commoncomponents/PasswordDialog.qml

src/commoncomponents/PhotoboothView.qml

src/commoncomponents/PreferenceItemDelegate.qml

src/commoncomponents/PresenceIndicator.qml