Make FD writing stricter

Resolves #850. #### Checklist - [x] I have read the [coding conventions](https://github.com/LostArtefacts/TR-Rando/blob/master/CONTRIBUTING.md#coding-conventions) - [x] I have read the [testing guidelines](https://github.com/LostArtefacts/TR-Rando/blob/master/CONTRIBUTING.md#testing-guidelines) - [x] I have added a changelog entry about what my pull request accomplishes, or it is an internal change #### Description Ensures FD functions are written in the correct order at write time rather than manually having to manage lists elsewhere. There are three entries in TR3 that fail the tests, where ceiling triangulation comes before floor. We just ignore those. Also improves ladder handling by ensuring multiple entries are squashed into one, and that null ladders are omitted.