Add an advanced preference page to manage the TXM startup command line (modifying TXM.ini)

Add an advanced preference page to manage the TXM startup command line (modifying TXM.ini).
Defines which arguments must be editable and create some input fields with checks for them.

Here is the default content of the TXM.ini (Windows version):

-Xms512m
-Xmx1024m
-Dfile.encoding=UTF-8
-Dorg.eclipse.ecf.provider.filetransfer.excludeContributors=org.eclipse.ecf.provider.filetransfer.httpclient4
-Dorg.eclipse.ecf.provider.filetransfer.retrieve.connectTimeout=6000
-Dorg.eclipse.ecf.provider.filetransfer.retrieve.retryAttempts=5
-XX:MaxPermSize=256m

We may also add these ones to easily tune the P2 updates:

-Dorg.eclipse.ecf.provider.filetransfer.retrieve.readTimeout=10000
-Dorg.eclipse.ecf.provider.filetransfer.retrieve.retryAttempts=30
-Dorg.eclipse.ecf.provider.filetransfer.retrieve.closeTimeout=1000

(from redmine: issue id 2031, created on 2017/02/10 by Sebastien Jacquot)