* KiCad: add *.kicad_sch-bak

As used by the new file formats for KiCad 6.0
See https://kicad-pcb.org/blog/2020/05/Development-Highlight-New-schematic-and-symbol-library-file-formats-are-now-the-default/

* Add *.kicad_prl to KiCad.gitignore

More info: https://forum.kicad.info/t/new-project-file-format/23705

Newer versions of KiCad call the schematics backup file `.sch-bak`.

This reverts commit 6ffcee9711.

See https://lists.launchpad.net/kicad-developers/msg38339.html and https://lists.launchpad.net/kicad-developers/msg38638.html

As described in commit c5a2ea1dd8 in the
kicad repository itself, the fp-info-cache file should not be checked
in to version control.

(See https://git.launchpad.net/kicad/commit/?id=c5a2ea1dd8b8f85f7524bbdaa17844f2324d02c5)

We shouldn't ignore -cache.lib files, because it causes missing components in your schema

http://kicad-pcb.org/help/file-formats/ specifically mentions this:

> `-cache.lib`: …​ a local copy of all the symbols used in the corresponding schematic, so that when the folder containing a KiCad project is copied to a different PC, the schematic can still be opened and printed and will still look the same as the original draughtsperson intended - even if that other PC does not have those symbols in its main libraries (or has symbols that coincidentally have the same name but are completely different).

Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

- *.ses files are generated by Freerouting (which is the partially integrated autorouter)
- *.dsn files weren't actually being ignored

According to their website, the correct capitalization is KiCad, not KiCAD.

These are two other filetypes that KiCad creates before overwriting something.

Add file for KiCAD EDA software