Change from Shell scripts to Bash scripts

The scripts need to be bash in order to use, for example, the following
line: `if [[ ${1} == "" ]]; then`

Simple one-line changes in all three files.
Change the example based on current operating system

This step is purely aesthetical (for now), and easier on non-OSX
developers who may see the '*.app' in the path as a file extension,
rather than viewing the target as a directory.

If needed, this can be expanded to add more operating systems in the
future.
Change target symlink depending on OS

Linux and OSX users will want the symlink to be in two different
locations, now the script will adjust accordingly.
Use proper exit codes in shell scripts

Proper exit codes are good practice.

Also, if a command fails somewhere in the middle of the script, it will
not proceed to the end of the script, outputting a message like "has
been restored to the installed configuration."
Simplify checking for existing symlink

It doesn't need to be that complicated, but may run into issues if they
have manually created folders or files named `dev`, rather than
automatically creating it as a link with `setup_for_hacking.sh`.

The exsting code was causing problems in Ubuntu anyway.
Correct "Example code"

By copy-pasting lines of code has come back to bite me! Good thing I
have an eye watching over me.
Merge pull request #4810 from IQAndreas/fix-shell-tools-for-linux

Fix shell tools for Linux