feat: taxonomy patch instead of re-generating

[alexgarel]

The goal is to be able to patch taxonomy text files instead of re-generating them completely.

This will avoid having a lot of changes that are not related to the real modifications made by a contributor.

For this we need to

• add a "modified" property to entries (to track modified entries)
• track lines location of entries (to know where to change the original file)
• keeping removed entries (because we need to remove them from the original file)

Relates to: #541 and #366

TODO:

• be able to patch taxonomy to generate the PR
• add tests
• add modified parameter in search
• add sort on modified parameter in search (sort is not done at all, for now)
• test it locally (see taxonomy: Update food_categories taxonomy openfoodfacts-bot/openfoodfacts-server#63)
• avoid repeating comments when replacing entry
• put children after parents, not the other way around
• on entry id change, also re-output children (especially the parent line)
• avoid adding empty line at end of file (it will accumulate otherwise)
• fix bug of simple entry creation, not being exported

[alexgarel]

I still need to do some testing !

[alexgarel]

I did a test openfoodfacts-bot/openfoodfacts-server#61 it results there are still some bugs that I have to solve.

The most problematic is if we change entry id. I think that along the entry last modification timestamp, I will also store the modified attributes, so that I know if entry id was modified.