using LodelContext.expose_modules instead of imports

Now able to run multisite and handled sites. Some addaptations are needed
because handled childs always return 404

Now we are able to generate dyncode for lodelsites and handled sites (
tested with only 1 handled site) using lodel_admin.py dyncode -a

Now it seems to work when no handled sites registered

Was missing : full plugin loading & hooks calls

Now following commands seems to work (on default multisite template) :
python3 lodel_admin.py dyncode
python3 lodel_admin.py dyncode -m sites_em.pickle -o sites_leapi_dyncode.py

Moved some function from plugin specific code to the bootstrap module
+ some bugfixes

In multisite loader utils

In this state I was able to insert a new site. But only the mongodb datasource
seems to have receive the query (inserted in DB but not created on FS).

Conflicts:
	lodel/editorial_model/components.py
	lodel/editorial_model/model.py
	lodel/plugin/plugins.py
	lodel/plugins/Makefile.am
	lodel/plugins/webui/templates/admin/editable_component.html
	lodel/validator/validator.py
Revert:
	lodel/validator/validator.py 3d51695ea6
		The hook HAS TO be registered even if not value !

Deleted hardcoded Object class name + adding support for varchar & text
in editable_component template

Now it seems to work. Tested using :
dummy datasource, no handled sites, ipython ui

Conditionnal plugins path given the context type (mono or multi site)

Now the directory tree looks like :
.sites_context/lodelsites/NAME/__init__.py
.sites_context/lodelsites/NAME/leapi_dyncode.py
.sites_context/lodelsites/NAME/lodel/ <- symlink

Only tested for lodelsites instance

The is_instance test on classes loaded from a pickle file is not
relevant :
lodel.editorial_model.components.EmClass != lodelsites.__loader__.editorial_model.components.EmClass

There is a problem left : when dyncode runs an error is triggered telling
that no active clases were found

Now both __loader__ and lodelsites contexts are using the same configuration
files and the same confspecs.

Now using mass_deploy and slim seems to work for a monosite