Add toolbar icon and shortcut for python console
Fix potential crash in random color ramp

Badly choosen values (eg max < min) could cause a crash. Now, values
are sanitised prior to generating the ramp colors.
Fix grammar
[FEATURE] Support drag and drop of python scripts onto QGIS window
Fix incorrect warning dialog appearing when creating new ramp

Previously a "not available" warning dialog would appear when
attempting to create a new color ramp using the categorised renderer.
[symbology] Add method for retrieving symbol layers as list