MIRTH-3475

Addressed problem when two server instances sharing the same database attempt to create channels at the same time. Both may obtain the same next local channel ID and the slower server will fail to insert the channel into D_CHANNELS with a duplicate key error.

Donkey's ChannelController.createChannel has been modified to detect a duplicate key exception and retry up to 2 more times to obtain the next local channel ID and create the channel.
MIRTH-3404: Added description label to the database tasks table.
MIRTH-3260: Added column control and right-click context menu to the channels table for showing/hiding columns (including the local channel ID). Visible columns are stored as user preference nodes, same as the message browser. The local channel ID is not part of the default visible columns.
MIRTH-3475

In Donkey's ChannelController, moved the retry logic added to createChannel() into the getLocalChannelId() method, since the server may also need to re-fetch the list of localChannelIds in the even that two servers are attempting to create donkey tables for the same channel.

Also added a 500 millisecond sleep in between retries to allow time for the server creating the donkey channel tables to finish.
Fixed some stat names
Added some missing stats
Removed some unnecessary stats
Issue: MIRTH-3332