Fixes #123 - Avoid caching song_id form parameter

[jaredmoody]

Restructure the add to playlist form so that instead of a list of buttons, each generating a form, we wrap the playlist buttons in a single form and each playlist button changes the form action when clicked to the proper playlist url.

This allows caching each button and fixes the bug where the song_id was cached with the html for each button.

[coveralls]

Pull Request Test Coverage Report for Build 1939012958

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 96.923%

---

Totals
Change from base Build 1933364594:	0.0%
Covered Lines:	693
Relevant Lines:	715

---

💛 - Coveralls

[jaredmoody]

In addition to the CI passing, I deployed this patch to my production environment and confirmed it resolves the issue.

[aidewoode]

Thanks, great implementation, I didn't know button has a formaction attribute before.

[jaredmoody]

Thanks! I learned about formaction recently too!