#8725 (Fast rendering) and #8733 (Better formating scales) and fix #8776

#8725: Fast rendering of LineStrings and Polygons pre-applying a view threshold filter to the geometries to render in qgis. View Table of test results in 'http://hub.qgis.org/issues/8725'

#8733: Better formating scales

#8776: Set the canvas color in 'qgsprojectproperties::apply()' before refresh