mediaprovider: Add theme support to Ringtone activity

Usage:

Intent intent = new Intent(RingtoneManager.ACTION_RINGTONE_PICKER);
intent.putExtra(RingtoneManager.EXTRA_RINGTONE_TYPE, RingtoneManager.TYPE_ALARM);
intent.putExtra(RingtoneManager.EXTRA_RINGTONE_DIALOG_THEME, R.style.CustomDialogTheme); <<< Add your custom dialog theme here
startActivityForResult(intent, 0);

Style Usage:

Define an style that inherits from an android base theme

<style name="CustomDialogThemeDark" parent="@*android:style/Theme.Holo.Dialog.Alert">

or

<style name="CustomDialogThemeLight" parent="@*android:style/Theme.Holo.Light.Dialog.Alert">

or define your own dialog style

Depends on http://review.cyanogenmod.org/#/c/61392

Change-Id: I409eba2674f68386cdd20b74fc3ea42b8e81d111
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>