SVGHMI: add static file serving feature.

Added two buttons to add and remove files.
Files are stored in project inside a directory named "static",
itself located in svghmi CTN instance files. Exemple :
exemples/svghmi_csv_json_img_table/svghmi_0@svghmi/static/
Files are transfered as "extra_files", but with a prefix
added to their name to avoid conflics.

     1

     2

                  <xsd:element name="Win32">

     3

                    <xsd:complexType>

     4

                      %(toolchain_gcc)s

     5

                    </xsd:complexType>

     6

                  </xsd:element>

     7