Paper updates: rename lastAgreeIndex to matchIndex.
Allow base.js, local.js imports in a browser.
Force debug in test_common.

The get* functions need _self to be exposed to be able to query
internal state.
Expose schedule/unschedule as options.
Refactor membership change to make it explicit ops.

- Make membership change into explicit ops (rather than implicit based
  on presence of a field): Cnew, Cold,Cnew.

- Make membership change a new exposed convenience method on the
  class: changeMembership(newServerMap, callback).

- Make all log additions go through addEntries routine so that we can
  always check and deal with membership changes in a single location.

- Add removeServer functionality to test_common and test_local.
Update comments to reflect current paper.