Adds license for `lineid_plot`

This license is for this software:https://github.com/phn/lineid_plot

I am merging it to S4.
Adds original lineid_plot

source:
https://raw.githubusercontent.com/phn/lineid_plot/master/lineid_plot.py
Adds surname of lineid_plot author
Change docstring

It will probably needs a better documentation.
Adds original source

I added the location for the original version of the lineid_plot
Remove run-as-a-script code

I don't need that `lineid_plot` run as a script.
Adds basic lined_plots to __init__

Then, they can be imported.
Adds example of use of line identification

This shows how to use the line identification codes.
Adds 'mod' to version

This is to inform that it is a modification from the original file.
Change to accept plot_line_id from S4

I have merged the `lineid_plot` code to S4. I had to adapt some stuff
to run Synplot with this.
Point user to the lineid_plot example
Remove dependency note.

I am merging `lineid_plot` into S4.
Remove `lineid_plot` from requirements

I am merging it to S4.
Adds `linedid_plot` merging to change log
Merge pull request #23 from gabraganca/lineid_plot

Merge `lineid_plot` project to S4