The views can specify js (and css) libraries to lazy load when
they are instantiated for the first time. The previous
implementation was too naive as it always loaded the specified
libraries in parallel. However, it may happen (e.g. gantt view)
that some of those libraries depend on other ones.
This commit implements a mechanism to handle libs dependencies
between each other. For instance, specifying:
js_libs: [
['a', 'b'],
['c'],
],
will load 'a' and 'b' in parallel, but wait for them to be
loaded before loading 'c'.
The new implementation still supports the old syntax. So,
js_libs: ['a', 'b', 'c'],
will load 'a', 'b' and 'c' in parallel.
Christophe Matthieu