Add a login screen for Android client

[mcicolella]

Our app has to interact with a Restful API (please see #1) served by our domotic framework so we need some info as

• restapi ip address
• restapi ip port (default 9111)
• username (default admin - NOT email)
• password (default admin)

So, after the splash screen, the app should show a login screen requiring the data if the user is logging
for the first time.
The data should be stored by the app avoiding the login process if it's not needed (for example the user logouts or wants to change connection data).
Currently connection data are managed by https://github.com/freedomotic/fd-android-client/blob/master/FDAndroidClient/src/main/java/com/freedomotic/freedomotic/network/FDSpiceService.java
After the login the app should show the main menu.

[paynemiller92]

I'm tackling this one! Let's go.