Fix encoding and formatting issues in 'nl' localization

These are issues i missed after my last review of !965 (merged)

• changed format of roadmap.yml back to UTF-8
• fixed various formatting issues in nl.yml and added missing keys
• change encoding of all user guides (nl) to UTF-8
• add missing guide

With this MR jekyll builds just fine.

added 3 commits

• 63a5522e...34f22596 - 2 commits from branch monero-project:master
• b3cae089 - fix encoding and formatting issues in 'nl' localization

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added 1 commit

• 22a0d3be - fix encoding and formatting issues in 'nl' localization

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resolved all discussions

mentioned in merge request !972 (merged)

merged

mentioned in commit f1f8aa5a