Dynamics option fixes

[dacap]

• Important Don't save/set the properties of all tools when the "Save in all Tools" is checked, we could use a shared tool section ([tool.shared.dynamics]?) for that. Because unchecking the "same in all tools" should not keep the dynamics on all tools.
• Use the matrix name/ID (instead of combobox index) to save the selected matrix for dynamic dithering
• Reset dynamics option from Preferences::resetToolPreferences() (there is a comment about this in pref.xml)

[dacap]

For the shared probably Preferences::tool(tools::Tool* tool) could support tool=nullptr (there is an ASSERT(tool != NULL); that should be removed in that case).