Startcenter: when screen is small make doc thumbails smaller

Change-Id: If4fbb66992318221a687710afa77fc98e4f111c3
Startcenter: double click opens file only once

Change-Id: I0d99a905cc8c94d39bfe802b2c597275c81f0b4f
fdo#71883 Startcenter: Re-introduce the 'Tools' -> 'Customize...' menu

Change-Id: I4d3993dc855c030f8c51fe2ce3d364240e241dff