[plugin] Fix typo
[plugin] Use imp module in order to retrieve info

This commit provides an alternative to the "cat/grep" method for retrieving the
information of a plugin.
Instead, it uses the imp module to load each module and then retrieve the
information directly from the plugin (like the description).

Plus, it prepares the merge for the issue #37 by providing a boolean describing
whether the plugin uses internets resources or not.
[plugin] Define an 'attr' dict for each plugin.

The 'attr' disctionary gathers the attributes of a plugin. Each new variable
will have to be declared into this dictionary.
For instance, the USE_INTERNET_RESOURCES becomes the 'internet_res' into the
attr dict.

Moreover, the attr dict is converted into json in order to be saved into the
database, in the attr column.