Ensure headers are strings

The headers of a response object should be strings, not unicode.

Here we ensure no non ascii char is provided as header and we convert
headers to string objects
Use 'autonomie' as default db name
Use a Node base model

In order to handle multi type relationships, we add a Node base model.
This model stores main fields and provide a OneToMany children/parent
relationship to itself, allowing us to link nodes as we want independtly
from their nature.
Add a File model to our database.
Add a traversal route to access files

Files acls are inherited from their parents.
Add a first view for our File model
Summary view for a file
Ref # 50 : configuration des types de fichiers

Les types de fichiers permettent de fournir une typologie uniforme des
fichiers adjoints aux documents, ainsi un document pourra être d'un type
custom ou d'un type prédéfini.
Add an invoicetable panel

Since both company_invoices and invoices templates contains the same
stuff, we place it in a specific panel.
Here we also add a "Attached files" column
Provide a snippet that allows to display attached files
Add a fileupload js script for the upload form

This script handles the filling of the description file when selecting a
document type in the file upload form.
Use LONGBLOB for file datas

LONGBLOB is specific to the mysql dialect, in the future, to allow
compatibility, LARGEBINARY should be used and replaced on the fly in the
initialize_sql utility for the mysql dialect.
Provide a humand readable format for file size
Display attached files in parent views

A parent is one of:
project
invoice
estimation
cancelinvoice
fix file type storage in main config

We store the file types in a list encoded as a json string and stored in
the "attached_filetypes" attribute of the main configuration.
Provide views for the file attachment

A File object can be attached to documents or projects.

We can :
Add
Edit
Delete
Download

a file.
Add views and links for file attachment

For each type of node (documents and projects), we provide a view to
attach a file.
We also add an actionmenu entry to all the associated pages.
Remove unnecessary code and fix little bug
Add a link for file attachment in invoice list
Filename in HTTP Headers fit the specs

In the http specs, the filename should be enclosed in double quotes.
Here we fix that point