Start 'develop' branch

For more information about the git policy here, see:
http://nvie.com/posts/a-successful-git-branching-model/
Initial latex output objects

The write function will be called from the star system which then
passes itself to the writer object, which in turn parses it into LaTeX.

Proper behaviour with the input function has to be ensured.
Fix minor compatibility issue with dict.keys()

The way the return of the keys method of dictionaries was used was
invalid python 3.4, which was now changed and is valid for both 3.4 and
2.7.
Add preamble and title output

The preamble and title will now be written to the file specified.
Add section on star system properties
Add writing of star properties
Write overview tables of orbits and terrestrials

Write the overview tables of all orbits of a planet system, followed by
a table detailing some characteristics of the terrestrial planets in
the planet system.
Add minor cosmetic changes

Change type of Asteroid Belt to "Ast. Belt" to save space in the table
of orbit contents.
Add several calcs and getters to asteroid belts
Add overview table of asteroid belts
Add symbols for quantities

Add different symbols for the quantities. For period the variable is P,
for orbital quantities the appropriate variable is R. Clarifications
are made via indices.

Also, only print a number for moons or moonlets in the overview table
if the number is not 0. This avoids a lot of meaningless entries.
Add detailed overview table of terrestrial planets
Remove second table

As the information of the second table got incorporated in the third,
remove it.
Rearrange tables

Rearrange tables so that the page is more efficiently used.
Make text formatting of overview table nicer

Use padding commands to align the alignment character (&).
Add naming of orbit contents

All orbit contents (and major moons) now have to get a name assigned to
them. This name will then later on be used in the output. As such it
can be customized (via the gui) later on at some point.
Add barebones functions for detailed dossier

Add the general overview of the program logic that will eventually
generate the detailed dossier for each planet system.
Add basic satellite enumeration of the planets

The detailed dossier will also contain major moons of planets, and will
list them after the planets.
Add terrestrial details in the detail-dossier
Add GasGiant to detail-dossier