(+) locks for chained animation

Now multiple instances of same plugin on same jquery selector will wait
each other in proper order.

For example we can use 'fade' plugin first to show object and then to
hide it. Two instances of plugin work on same object in different time
intervals.

In current realization interpolation looks like:
^
|                  *
|                   *
|          *-------  *
|         *           *
| -------*             *
|                       *---------
+---------------------------------------> t

----  interpolated value
****  value provided and animated by plugin

TODO: still no interpolation in gaps between plugins.