Asset editor improvements

[fredsa]

• Reformat affected files prior to other commits
• Fix asset undo (Asset Editor doesn't undo properly #213)
• Implement asset editor redo
• Create distinct undo for each asset edit
• Limit asset editor to undos in current session
• Fix stacking "no more undo/redo" alerts
• Ignore ';;' that is a new ';;{…};;' asset block
• Asset editor displays line number ranges and header
• Click line number range to jump to highlighted lines
• Show errors for assets with incorrect number of values
• Fix bad edits when source has different length values
• Fix length new data values written
• Align thumbnails to the top to prevent visual jumps
• Dismiss highlighted lines on user interaction
• Replace affected asset range, not entire file contents
• Asset undo inside source editor shows affected lines
• Likely fixes [Possible bug] Asset editor gets reset #62

[fredsa]

Updated PR title and the initial comment

[fredsa]

Rebased commits on origin/master

[fredsa]

Last two commits add:

• affordance for asset line numbers in asset editor
• clickable asset editor decorations in source code

[fredsa]

Rebased on origin/master

[fredsa]

• Fix validateAssetData, add max reachable offset
  calculation, fixes NES issues with chr_generic.s
• Add validateAssetData support for rletag
• Fix broken asset editing and undo when asset source
  has not been previously opened manually, for example
  when reloading the #asseteditor page directly
• Fix palette color undo/redo

[fredsa]

• Implement #asseteditor/filename/lineno support,
  and highlight selected asset on navigation

[fredsa]

• place the "asset editor" decoration after header instead at the end of the line

[fredsa]

Rebased on origin/master

[fredsa]

Screenshots:

[sehugg]

Very cool! Glad to see Asset Editor getting some love. Lemme take a closer look at everything and merge soon. Have you been using it succesfully in your projects?

[fredsa]

Thanks. This PR was a bit of a treasure hunt adventure, to find all different things it supported across platforms.

I've spent a fair bit of time with the undo/redo functionality, and how it interacts with editor edits. One design choice was that when you navigate to the asset editor its undo/redo stack is reset. That way extra undos from the user won't result in surprises (i.e. source code edits unrelated to the asset editor being undone and lost to the sands of time).

Open to more ideas to improve the UX. Please feel free to change the CSS. I really like the filename pill at the top of the asset editor cards. I don't feel that my visual additions to the asset editor and text editor look as good as that aesthetic.

[sehugg]

Undo/redo resetting makes sense for this case, glad you figured it out. I'll go ahead and merge and any minor issues can be cleaned up later. Thanks! Looks good!