This PR improves the registers widget UX by adding multi-row selection and better copy/paste support.

Previously, the widget only allowed single-cell selection which made it annoying to copy, paste, modify and work with multiple registers at once. Now, a user can select multiple rows using Ctrl+Click and Shift+Click, such as any standard list.

• When selecting multiple, you can "Open Each in New Pane" which will go through each and open them as a new pane.
• I've made it so you can "Copy Row" using Ctrl+Shift+C which will copy the selected row(s) in name: 0xvalue (hint)\n format.
• Setting to zero works on all selected registers instead of just one
• Select All is now a right-click feature to give that standard feature

Actions that only make sense for a single register (Edit Value, Jump to Address, Paste, etc.) are only available when working with one register, and disabled on multiple rows.

Along the way, intx::from_string I found doesn't like any non-numeric text and will cause Binary Ninja to crash when pasting. I've fixed this with a try-catch.