Add a prototype of a class to hold a list of lines.

Stuff to consider:

- The current HTM implementation has level 0 with 8 subdivisions
  already, instead of level 0 = the whole sky. This means that if we
  want to not break up a line, we have to write two versions of the
  code, one using HTM and the other not.

- We may need to have a subclass of this class that holds lines with
  proper motion (constellations).

- In the old LineListIndex SkyComponent, the way that it uses the HTM
  is as follows: first, it stores a bunch of small lines, and then it
  determines for each line what trixels are covered. Thus one can
  request a list of the lines that cover a set of trixels.

  However, this isn't so great for our purposes. We want to store as
  much as possible in a single buffer and work with all the points at
  once. So we are specifying our lines differently: we hold an array
  of all the vertices used, and then we have a bunch of arrays of
  integers that are indexes into the first array. These represent our
  lines.

  What we should do is have some code that takes as input a buffer
  and a list of index arrays, and splits the lines on trixel boundaries.
  This way, we can get just the lines and buffers needed for the trixels
  we want, but without having to have more than one array of vertices
  per trixel.

CCMAIL: akarshsimha@gmail.com