Improve sharing

Previously, the share page can handle only a limited number of shares and only one of each type.
Now the configuration has been change to be more flexible and allows an unlimited number of shares.
The share description is located in an array and the share configuration is stored along with the
user configuration.

#401

Note: I tried to include the specific javascript code in a separate file but I did not succeeded to
import it.
Note: I tried to run the install script to see what happens on configuration and it appears to be overridden. So I decided to keep the script as is.