feat(docs): various improvements

- removing spaces at end of line
- fixing spelling and grammar mistakes
- making sure 'Vikunja' is spelled the same way everywhere
- prefer using editors word wrap instead of hardcoding word wrap in markdown (reason: different word wrap per editor & end of line space)
- add newline add end where missing
- remove double colon at end of headlines
- remove unnecessary indention
- make sure code blocks and headlines etc always have an empty line around

docs/content/doc/setup/backups.md

@@ -56,4 +56,4 @@ For more information, please visit the [relevant PostgreSQL documentation](https
 
 ### SQLite
 
-To back up sqllite databases, it is enough to copy the [database file]({{< ref "config.md" >}}#path) to somwhere else.
+To back up sqllite databases, it is enough to copy the [database file]({{< ref "config.md" >}}#path) to somewhere else.