Elevate permissions on directory access and filepath comparison

[archnode]

Closes #103

There are a few instances where we have to be more liberal with elevating permissions to get consistency when using different owners.

• On directory access as in [BUG] Dotter doesn't elevate if it can't read a directory #103
• On comparing symlink targets
• On running with --dry-run

[archnode]

This leads to further headache when having to delete changed symlinks. I added further changes to the target cache handling.

I'm not sure if my usecase that necessitates this makes sense for dotter in general:

• User A (with sudo) checks out config repo in /usr/local/share
• User A uses dotter to deploy config to system, user A homedir and user B homedir.

Probably a viable workaround would be:

• Use sudo with dotter in combination with hardcoded paths and owners OR
• Run dotter for each user seperately with different local.toml files

I still think the changes make the system with privilege elevation more consistent, but I'm unsure if that is something dotter should concern itself in general.