scheduler: tasklet registry addition

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
jsonalchemy: default values for subfields

* Fixes jsonalchemy ignoring default values when the main field is
  present but not one of the subfields. (closes #34)

Signed-off-by: Esteban J. G. Gabancho <esteban.gabancho@gmail.com>
assets: fix some missing url_for("static")

Signed-off-by: Yoan Blanc <yoan.blanc@cern.ch>
Reported-by: Jan Åge Lavik <jan.age.lavik@cern.ch>
assets: less flavor of bootstrap

* Installing less and grunt-contrib-less.

* Adding the filters parameter on the assets.
  `{% css "foo.css", "00-bundle", "less" %}`

* Adding one extra configuration key: LESS_BIN which must be pointed to
  lessc: e.g., node_modules/grunt-contrib-less/node_modules/.bin/lessc

Signed-off-by: Yoan Blanc <yoan.blanc@cern.ch>