move various methods to the open source client

This commit moves these methods to the open source hypernode-api-python client:
```
get_app_info_or_404
get_next_best_plan_for_app_or_404
validate_app_name
get_slas
get_available_backups_for_app
get_app_eav_description
set_app_settings
get_app_configurations
get_product_info_with_price
get_whitelist_options
get_whitelist_rules
get_current_product_for_app
check_payment_information_for_app
get_active_products
check_xgrade
xgrade
order_hypernode
```

There is some code in here that's slightly incongruent, but that's an
artifact of where this came from. I added docstrings with usage examples
and refactored out some of the django specific exceptions (Http404) and
replaced those with RuntimeError so that the client doesn't make any
assumptions about being ran in a Django application.

Author: vdloo

README.md

@@ -27,24 +27,44 @@ pip install -e git+https://github.com/byteinternet/hypernode-api-python.git@mast
 ```
 Of course you might want to put that in a `requirements.txt` file in your project instead of installing it manually.
 
+###  Performing API calls
+
 Then to use the API client you can test out an example request in your Python repl:
-```bash
-[1]: from hypernode_api_python.client import HypernodeAPIPython
+```python
+from hypernode_api_python.client import HypernodeAPIPython
 
-In [2]: client = HypernodeAPIPython(token='yoursecrettoken')
+client = HypernodeAPIPython(token='yoursecrettoken')
 
-In [3]: response = client.get_app_flavor('yourhypernodeappname')
+response = client.get_app_flavor('yourhypernodeappname')
+
+response.json()
+{'name': '2CPU/8GB/60GB (Falcon S 202202)', 'redis_size': '1024'}
+```
 
-In [4]: response.json()
-Out[4]: {'name': '2CPU/8GB/60GB (Falcon S 202202)', 'redis_size': '1024'}
+Using the Hypernode-API you can automate all kinds of cool things like configuring settings:
+```python
+client.set_app_setting('yourhypernodeappname', 'php_version', '8.1').json()
+{'name': 'yourhypernodeappname', 'type': 'persistent', 'php_version': '8.1', ...}
+```
 
+To even performing acts of cloud automation, like scaling to the first next larger plan:
+```python
+client.xgrade(
+    'yourhypernodeappname',
+      data={
+          'product': client.get_next_best_plan_for_app_or_404(
+              'yourhypernodeappname'
+          ).json()['code']
+      }
+)
 ```
 
+
 ## Development
 
-To run the unit tests you can us `tox`:
-```
-tox
+To run the unit tests you can use `tox`:
+```bash
+tox -r
 ```
 
 ## Related projects