Simplify tedium operation and make more conservative.

[aomarks]

This makes tedium more conservative, and simpler to control.

• Passes and repos must now be specified explicitly. Previously there was a set of automatic passes, and repos were fetched from PolymerElements.
• --baseBranch is the branch we will clone from and apply changes to (default "master").
• --workBranch is the branch we will commit and push to, and maybe create (default "tedium"). It can be the same as --baseBranch if you just want to commit directly, but you'll also have to set --noPr in this case or you'll get an error.
• We now create PRs by default instead of magically. The PR will merge workBranch into baseBranch. Set --noPr to not create a PR. Set --prTitle to set a custom PR title.
• By default only 1 repo is now pushed unless you ask for more (previously unlimited unless you asked for fewer).

[e111077]

Does this remove functionality to run on all elements? If so, can that still be an option rather than the default? Probably just read repos from a txt