Create CatchupActor, CatchupSupervisor

Reworking catchup process. Mutate window size based on historical
success/failures, similar to TCP slow-start / congestion-avoidance.
These actors provide the basis for this, and included here are the
config options we'll need. Nothing's hooked up.

Also included are the new messages it'll use.
Wire in new catch-up algorithm

Wire the new catchup actor and supervisor into place. Includes reworking
a *lot* of the way the PaxosStateBridge works, but hopefully putting it
in a much more understandable state than before. Also includes changing
SiriusPersistenceActor so that it uses the new LogSubrange methods.
Remove old catch-up remnants

Remove GapFetcher*, and the messages we used for sending around
subranges of logs. Don't need 'em anymore!
add contributors.md file
Merge pull request #76 from tbarker9comcast/create-contributing-page

add contributors.md file
Add MBean monitors for window, ssthresh

This stuff will be very helpful to have accessible through JMX. You
could conceivably detect network badness by a lower-than-normal
ssthresh, and it might be fun to graph window. Just suggestions, YMMV.
Simplify Catchup Request logic, more config

Eliminate CatchupActor in favor of ask(). In addition, make more of the
catchup params configurable, and add some explanatory documentation to
the CatchupSupervisor.
Merge pull request #75 from clinedome-work/rework-catchup-algorithm

Rework catchup algorithm
Make akka max-frame-size configurable

Also, make it actually do something. We currently specify it in a
non-functioning way for the version of akka we're using. Apparently the
key for that piece of configuration changed with the versions.

128K is the default for Akka, which is how it's been de facto configured
since the last release. Changing the default to 1024K, which is a little
more real-world useful for applications using Sirius, particularly WRT
catchup messages.

Also, make send/receive buffers scale with max-message-size.
Merge pull request #72 from clinedome-work/akka-max-frame-size

Make akka max-frame-size configurable
Release 1.2.1
This release contains a fix for issue #48, where very slow networks coupled with large catchup windows could cause unbounded memory usage in cluster nodes.

New Features
======
d64c17e Make akka max-frame-size configurable
00e94b0 Simplify Catchup Request logic, more config
525b321 Add MBean monitors for window, ssthresh

Bugfixes
=====
688699f Remove old catch-up remnants
3534071 Wire in new catch-up algorithm
229dbc7 Create CatchupActor, CatchupSupervisor
564dbb4 Increase FullSystemITest membership timeout
1457e69 Replica should ignore out-of-date DecisionHints
a3fefb9 Fix tty restoration logic in sirius-standalone

Documentation/Project Maintenance
=====
381384c add contributors.md file
52d8509 getRandomMember returns Try instead of Option
adf343e fix typos
49e383f Updated pom.xml to support Maven-Repo standards
689db44 Disable parallel testing
41bf952 fix travis badge
8c5f976 Small cleanup of SiriusFactory
a59f764 SiriusConfig.getProp default to call by name
9a210d4 add CLA link to contributing page
415bab1 Fix README typo
e85ea7e give credit to lazybones on NOTICE page
4ac7d93 Instructions for contributors re: CLA.
b7cab2e cleanup unit tests
2d788db Bump version to 1.2.1-SNAPSHOT
Merge pull request #80 from mbyron01/Release-1.2.1

Release 1.2.1