chan(*): normalize script names

[D-Brox]

Purpose

We don't need the files to have *-local.sh.

Approach

Renames download.sh to get-pacscript.sh and download-local.sh to fetch-sources.sh, as it is more descriptive.
Renames install-local.sh to package.sh, since the -B flag exists.
Renames error_log.sh to error-log.sh, an almost 3 year old mistake by me (in #146)
Renames build-local.sh to build.sh because the -local is redundant.

Replaces all mentions to the filenames in the code

Progress

Done

Checklist

• I confirm that I have read the contributing guidelines, and this pull request is abiding by all the clauses stated in the guideline.

[oklopfer]

can you also do:

shfmt -bn -ci -sr -s -i 4 -w pacstall misc/scripts/*.sh
chmod +x misc/scripts/*.sh

feel free to say no and save it for the next PR, but it should be the next thing to be done