Comment 1 for bug 1080578

Currently user have to switch between different keyboard layouts by shortcut (for example Shift+Alt or Shift+Shift) or by using keyboard layout indicator on DE's panel, which is slowdown text typing, especially text with many terms in English. Example: https://www.linux.org.ru/news/proprietary/13079230

For users with three keyboard layouts (for example English/Ukrainian/Russian) this issue is much more critical, since they need to switch between keyboard layouts more frequently.

Changing switch keyboard layout to Win button is no-go for tablets that occasionally used with keyboard dock with touchpad, because Win button is actually useful in Gnome Shell.

I propose to:
1. In Small keyboard layout add button for switch to next keyboard layout to lower right corner.
2. In Compact keyboard merge Abc and 123 button into one button that switch between two modes.
Move Settings button up to set lower right corner free.
Add button for switch to next keyboard layout to lower right corner.

Potentially, it would be cool to display which keyboard layout is next on this button (like Eng/Rus) but in my opinion this is separate matter, and simple button that just switch to next keyboard layout is good enough for now.

I also thinking about keyboard layout switching methods that doesn't alter Onboard's own keyboard layouts, like swipe over backspace. Unfortunately, touchsceen quality in cheap tablets is low (or not properly calibrated by vendor, while faulty calibration data flashed into hardware (seen with Goodix) or, like in Silead case, provided as not-editable firmware file that loaded by driver) and there could be detecting issues around corners that doesn't affect tap events, but could be frustrating if swipe require two-three attempts to get detected by application. So, switch keyboard layout by swipe over backspice is also nice thing to have (and most likely will work fine on tablets with proper touchscreens) but not something that can replace button for switch between keyboard layouts.