Add CodeMash, QCon, and Scala Days conference data

[okentao]

Adds current public entries for CodeMash, QCon, and Scala Days to the conference dataset.

Claims:
/claim #4
/claim #10
/claim #11

Source notes:

• CodeMash: official CodeMash site.
• QCon: official QCon site and C4Media organizer site.
• Scala Days: official Scala Days site and Scala Center organizer site.
• Used conservative values where public SEA, reimbursement, or compensation commitments were not found.

Verification:

• git diff --check
• table row column-count check
• source link checks for CodeMash, QCon, C4Media, and Scala Days returned HTTP 200; Scala Center page timed out locally but is the public organizer site.

[okentao]

This PR also includes the requested rows for the other two open bounty issues covered by the same README change:

/claim #10
/claim #11