Standardize the icon used for the reset button

[DelazJ]

using https://github.com/qgis/QGIS/blob/master/images/themes/default/mActionUndo.svg for all reset button
Fixes qgis/qgis3_UIX_discussion#36

[nirvn]

@DelazJ , I'm +1 for the evis-related .ui changes, but I'm not sure it's that great to use a single icon to represent undo (i.e. going one step back) vs. clear/reset (i.e., wiping out all of the previous steps).

[DelazJ]

I'm not sure it's that great to use a single icon to represent undo (i.e. going one step back) vs. clear/reset (i.e., wiping out all of the previous steps)

Me neither! Do you mean there should be a new reset button (out of my skills) or is there already one that suits?
I guess some of the Options dialog reset buttons will also need updates in that case.

[DelazJ]

Reverted changes on the Refactor Field dialog

[m-kuhn]

@nirvn can you take the lead here?

[nirvn]

@DelazJ , looking good. I've merged this as it is definitively a step in the right direction. We should eventually try and come up with a reset icon, but that can wait.

Thanks.