The proxy must be able to persit some channel

The proxy must be able to persit some channel: we start to use to proxy to capture messages from/to simulators. Those channel must be open in permanence: they must be opened when the proxy start.

The list of persistant channels will be stored in a csv file on the file system. Format and content of the csv is the same as the one used for importing/exporting configuration.
At start-up, the Proxy will look at the specified location (application preference to be added) to check whether the file exists. If so, then, it will open the listed channels.

Todo
1. Add a new application preference that contains the absolute path to the CSV file where the persistent channels are listed.
2. Add a boolean to the Channel class => persistent
3. Add a checkbox on the Channel creation page in the GUI. If the box is checked, then the Proxy shall write the details in the CSV file once the channel is started (it ensures that only valid configurations are stored in the CSV file)
4. Add an icon in the list of channel to inform the user that a channel is persistant
5. Rename the "Stop" channel button into "Destroy channel"
6. For persistant channels, add a "Delete channel" button ==> it will remove the entry for the CSV file
7. When the Proxy starts, it shall read the csv file and start the channels
8. Add a column to the csv file 'persisted'
9. Update the export feature to populate the persisted column
10. Update the import feature, if the 'persisted' column is set to true for the entry, the entry shall be added to the csv file that lists all the persisted entries.

NB. Make sure not to introduce duplicate entries in the csv file (proxy port shall be unique)