Add slider to change mask radius
Increase visibility of edit brush outline
Add a color box to the layer selectors
Improve brush rendering.
First attempt to build a win32 version
Remove toolbar border
US25: Reduce the differences between Linux and Windows

- Reduce the number of changes needed between the Linux and Windows version.
- Add the example toolchain file for W64.
- Add a summary of the instructions to build the dependencies with MinGW-w64.
US25: Updated build method

- Toolchain files stripped to minimum.
- Update build guide with complete explanations and commands.
- Fix translation.
US25: Fix indentation
Fix small problems with the Windows version.

- Integrate the toolbar icons in the executable.
- Fix the storage of settings with an organization name.
- Fix some default margins that get different values in each platform.
- Move the toolbar to the top of the window.
- Add a tooltip to the layer buttons to show the EV steps relative to the least exposed image.
US44: Add a slider for the preview brightness

- Add a slider to the main toolbar to control the preview brightness.
- Refactor the main window to contain two toolbars, Tools and Layers.
- Both toolbars are movable to any position.
- Add tooltips for the slider widgets.
- Add repaintAsync method to PreviewWidget, that cancels the last background repaint and starts a new one.
Add a save default DNG options feature.

- The DNG options can be saved as the default values for the next images.
- The file name for the mask can contain tokens that are replaced by the name and directory of the output file and the least exposed image.
Add website URL to README