Unify variables’ default value presentation with other values

[MattiSG]

All values in the legislation explorer are represented as <samp> except in the default value part.

This changeset unifies this presentation and localises number formatting.

It also brings:

• A partial refactor of the Variable view, fixing indentation and removing an unnecessary dependency.

Before

After

(example from https://fr.openfisca.org/legislation/irpp)

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Depends on #149.