How to improve brush shortcuts for mouse and tablet use

[Frozen Death Knight]

It's nice that brush rotation is now supported by using the left and right arrow keys on your keyboard, but I think we can go a bit further than that to make these commands easily accessible with a mouse and especially on tablets like a Wacom or similar brands.

With the current mouse commands for brushes, you have these at the moment which I divided up in L click and R click:

• L click to draw a stroke.
• Shift + L click to make straight lines (thanks for adding this btw!).
• Alt + L click to colour pick.
   
• Alt + R click + L click to change brush size and/or hardness.

Here's how I think the brush commands in the future should look like:

• L click to draw a stroke.
• Shift + L click to make straight lines.
• (ALTERED) Alt + L click to colour pick based on the settings that it remembers from the Colour Picker tool. Right now if you change it from Global to Current Layer, your brush will not remember this setting like in Photoshop.
• (NEW) Ctrl + L click to open up a panel of different types of rulers that your brush can use to follow its path. For instance, one ruler would be a circle that you can change size, form, rotation, and position on the canvas that your brush will follow until you deactivate it. Check out the plug-in Lazy Nezumi Pro for reference to get a better understanding of this feature.
   
• (NEW) R click to open up some form of a brush manager to select brushes on the fly. Could be something else brush related like a floating colour wheel (or maybe both? ;D), but I think a brush manager would suffice here.
• (NEW) Alt + R click to change brush size only.
• (NEW) Shift + R click to change brush hardness only.
• (NEW) Ctrl + R click to change brush rotation only.

The R click commands especially would the most useful changes and probably the easiest to implement. It would make using a tablet with pens a lot easier to work with and more user friendly.