update customise interactions nodebook

[barneydobson]

Summary

• Update customise interactions to use extensions
• I have added each extension in its own separate module to make them easier to understand (although mentioning these could be in the same module).
• These modules I have reproduced in html details. My preferred option would be to use this API like in this, which feels much tidier in terms of formatting and more sustainable as code does not need to be reproduced. But as we discussed in SWMManywhere - it seems that mkdocs-jupyter can't access the API docstrings. I could use a yaml codeblock, which would include the python formatting, but it looks super weird as it is formatted differently from the notebook and can't be stored in a details. Thus, I think this is the best way, but am open to suggesstions.
• I have done the same way to find this scripts folder as in the another demo with os - though it's a bit ugly. Obviously __file__ would be preferrable, but this doesn't seem to work with mkdocs-jupyter.
• Bit better default behaviour for river_discharge_order.
• a few broken hyperlinks
• I'm going to let this close the issue #112 - the river reservoir tutorial needs a lot of work that is not really related to extensions

Fixes #112

[barneydobson]

@dalonsoa will update tabulate... ~I will check but I'm pretty sure the relative links seem to work differently in mkdocs-jupyter~

[barneydobson]

@dalonsoa yep when I serve this locally the link works. I didn't figure out why but I'm sure when I first made the documentation while the 'normal' mkdocs way of referencing (reference-model.md#wsimod.orchestration.model.to_datetime) worked locally I seem to remember it not working when deployed..

We can change every link to remove these warnings... but there's a chance it won't work when deployed and we'll have to change them back. On the live website the warned link still works