Fix for exhausting the Neo4j Server ThreadPool with too many selectors, so that no acceptors are available

* extracted HttpConnectorFactory
* SslConnectorFactory inherits from it to use the same approach
* Jetty makes wrong choices for selectors (numcpu instead of numcpu/2), so we have to provide explicit counts for selectors and acceptors
* Determine number of relevant CPUs by taking the size of the thread pool into account
* Add some other performance related configurations from the Jetty docs
Merge pull request #2199 from jexp/server-threadpool

Fix for exhausting the Neo4j Server ThreadPool with too many selectors, so that no acceptors are available
Fix memory leak in XaResourceManager.

The txOrderMap was initially only meant for and used by recovery. However, HA started
injecting transactions using the same recovery code as well. This meant that the
txOrderMap was steadily accumulating data, but never got cleared, because the clearing
only happened at the end of recovery.

This memory leak has been fixed by removing the txOrderMap completely, and instead let
the TransactionStatus objects know how to order themselves.

Conflicts:
	community/kernel/src/main/java/org/neo4j/kernel/impl/transaction/xaframework/XaResourceManager.java
	community/kernel/src/test/java/org/neo4j/kernel/impl/transaction/xaframework/TestApplyTransactions.java
Merge pull request #2212 from cleishm/cherry-xa-leak

Cherry-pick from 1.9-maint: Fix memory leak in XaResourceManager.
Merge commit '7f0838f' into 2.0-merge-1.9

Conflicts:
	community/server/src/main/java/org/neo4j/server/web/Jetty9WebServer.java
Merge commit '9621470' into 2.0-merge-1.9
Merge commit 'b887012' into 2.0-merge-1.9

Conflicts:
	community/kernel/src/test/java/org/neo4j/kernel/impl/transaction/xaframework/TestApplyTransactions.java
Merge commit '3c6e81d' into 2.0-merge-1.9