Add template files to package

[kvid]

Specify all HTML files under templates folder to be included as package data files.

Is this sufficient to fix #345? Some sources claim that include_package_data=True also is needed, but preliminary testing at my Windows setup seems to prove otherwise. I would prefer that some ohers could confirm at different platforms and versions.

• Verify in Windows
• Verify in Linux
• Verify in macOS

[kvid]

Suggested test procedure:

cd {some empty folder}
python3 -m venv .venv
source .venv/bin/activate
git clone https://github.com/wireviz/WireViz --branch=fix345
cd WireViz
pip install .
cp examples/demo0?.yml ..
cd ..
rm -rf WireViz
wireviz demo0?.yml
which wireviz

or at Windows:

cd {some empty folder}
python3 -m venv .venv
call .venv/Scripts/activate.bat
git clone https://github.com/wireviz/WireViz --branch=fix345
cd WireViz
pip install .
copy examples/demo0?.yml ..
cd ..
rmdir /s /q WireViz
wireviz demo0?.yml
where wireviz