Part of meta issue987.

Renaming this issue because we want to extend its purpose. Besides making it consistent with coding conventions, we would also like to have shorter functions, more suitable variable names, and bring comments up to date. All of this should not affect the overall functionality in any of the landmark heuristics.

Since these changes are mostly independent between different parts of the code, we discussed offline that we want to approach this in three stages:
(1) landmark graph and landmarks
(2) landmark heuristics and status manager
(3) landmark factories

If he gets to it, Remo is going to start with (1) as part of the sprint that started today.

Link to meta issue.

I think the idea is also to rename variables and methods for better readability, as well as to re-order methods of classes.

Much of the landmark code violates the coding conventions. In this issue, we'd like to make the landmark code consistent with the coding conventions without changing any functionality.