[SPARK-1182][Docs] Sort the configuration parameters in configuration.md

Sorts all configuration options present on the `configuration.md` page to ease readability.

Author: Brennon York <brennon.york@capitalone.com>

Closes apache#3863 from brennonyork/SPARK-1182 and squashes the following commits:

5696f21 [Brennon York] fixed merge conflict with port comments
81a7b10 [Brennon York] capitalized A in Allocation
e240486 [Brennon York] moved all spark.mesos properties into the running-on-mesos doc
7de5f75 [Brennon York] moved serialization from application to compression and serialization section
a16fec0 [Brennon York] moved shuffle settings from network to shuffle
f8fa286 [Brennon York] sorted encryption category
1023f15 [Brennon York] moved initialExecutors
e9d62aa [Brennon York] fixed akka.heartbeat.interval
25e6f6f [Brennon York] moved spark.executer.user*
4625ade [Brennon York] added spark.executor.extra* items
4ee5648 [Brennon York] fixed merge conflicts
1b49234 [Brennon York] sorting mishap
2b5758b [Brennon York] sorting mishap
6fbdf42 [Brennon York] sorting mishap
55dc6f8 [Brennon York] sorted security
ec34294 [Brennon York] sorted dynamic allocation
2a7c4a3 [Brennon York] sorted scheduling
aa9acdc [Brennon York] sorted networking
a4380b8 [Brennon York] sorted execution behavior
27f3919 [Brennon York] sorted compression and serialization
80a5bbb [Brennon York] sorted spark ui
3f32e5b [Brennon York] sorted shuffle behavior
6c51b38 [Brennon York] sorted runtime environment
efe9d6f [Brennon York] sorted application properties