Hi !
a very late answer for Kodi 16 for Windows and Linux
You can add a Toggle Full Screen button by editing the Home.xml file (with Notepad++ e.g.) in
-Windows: Kodi\addons\skin.confluence\720p\ (see in Program File)
-Linux: /usr/share/kodi/addons/skin.confluence
You have to find in the file these lines:
<control type="image">
<description>Favourites Icon</description>
<left>5</left>
<top>5</top>
<width>35</width>
<height>35</height>
<aspectratio>keep</aspectratio>
<texture>icon_favourites.png</texture>
</control> (line 1154 in my file, maybe different. Find <description>Favourites Icon</description> in your file)
and insert these lines to create the button:
<control type="button" id="22">
<description>PleinEcran push button</description>
<left>110</left>
<top>0</top>
<width>45</width>
<height>45</height>
<label>1036</label>
<font>-</font>
<onclick>ToggleFullScreen</onclick>
<texturefocus border="5">floor_buttonFO.png</texturefocus>
<texturenofocus border="5">floor_button.png</texturenofocus>
<onleft>20</onleft>
<onright>20</onright>
<onup>9002</onup>
<ondown>9003</ondown>
</control>
<control type="image">
<description>Plein Ecran Icon</description>
<left>115</left>
<top>5</top>
<width>35</width>
<height>35</height>
<aspectratio>keep</aspectratio>
<texture>GoFullscreen.png</texture>
</control>
and you could change the value of the Rss feed <width> to 1090 for a perfect modification (find <control type="rss">, it's line 1084 in my file)
This is a useful mod to control Kodi with a wireless mouse !