ESLint tweaks

[doubleedesign]

• Turn off the automatic "no-irregular-whitespace" rule that seems unnecessary yet problematic
• Add detail to indent rules so the auto-fix will indent things a bit more neatly and not allow extra or missing indents (e.g., function body should be one indent in from the lines that open and close the function declaration)
• Remove image extensions from the structure check because that runs the regular lint as well, tries to interpret them as code, and has a bad time
• Add js and jsx extensions to the base check, because some people aren't using TypeScript
• Add auto-fix script to package.json