Add interval annotations

[gchudnov]

Add interval annotations that can be displayed:

now

                  [******************]   | [5,10]
  [**********************]               | [1,7]
                  [******]               | [5,7]
--+---------------+------+-----------+-- |
  1               5      7          10   |

if annotations are added:

                  [******************]   | [5,10] : a
  [**********************]               | [1,7]  : b
                  [******]               | [5,7]  : c = a ∩ b
--+---------------+------+-----------+-- |
  1               5      7          10   |