Move from using setup.py to requirements.txt for plugins

[tsalemink]

The setup.py scripts we are using for the MAP-Client plugins are outdated. These scripts are currently only being used to extract plugin dependencies, so each could be replaced with a requirements.txt file. Since we don't actually want to pip install the plugins, there is probably no point in updating the configuration scripts to pyproject.toml.

The following functions and their usage will need to be updated to handle requirements.txt instead of setup.py:

mapclient/src/mapclient/core/managers/pluginmanager.py

Line 182 in b167e44

def installPackage(self, uri):

mapclient/src/mapclient/core/managers/pluginmanager.py

Line 197 in b167e44

def extractPluginDependencies(self, path):

mapclient/src/mapclient/tools/pluginwizard/skeleton.py

Line 80 in b167e44

def _writeSetup(self, target_dir):