App.backend.Connection: handle content type for JSON and text(other)

* mw/sendFile: coding style fix

Signed-off-by: Oleg Verych <olecom@gmail.com>
App.create(): use `Ext.undefine` to fix `initComponent()` override

Signed-off-by: Oleg Verych <olecom@gmail.com>
App.reload() `App.Cladd.__noctl`: reload only view (no controller)

* noop refactor: url = App.backendURL
* ctl_loaded, ctl_not_loaded: hoisted and `ctl_not_loaded()` is used

Signed-off-by: Oleg Verych <olecom@gmail.com>
App.view.desktop.BackendTools: delete `xtype: 'sg-ct'`

This Class is loaded by its class name via backend's auth stuff.
Thus no `xtype` shortcuts must be used.

Signed-off-by: Oleg Verych <olecom@gmail.com>