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.

_data/lang/nl/roadmap.yml

@@ -43,7 +43,7 @@
     - name: Versie 0.10.1 Wolfram Warptangent
       date: 2016-12-14
       status: completed
-    - name: Officile GUI bta 1
+    - name: Officiële GUI bèta 1
       date: 2016-12-22
       status: completed
 - year: 2017
@@ -69,7 +69,7 @@
     - name: Fluffy blocks
       date: 2017-09-07
       status: completed
-    - name: GUI niet meer bta
+    - name: GUI niet meer bèta
       date: 2017-09-10
       status: completed
     - name: Netwerkupgrade voor minimale ringgrootte van 5 en verplichte RingCT-transacties
@@ -89,7 +89,7 @@
     - name: Nieuw proof-of-workalgoritme CryptoNoteV7
       date: 2018-04-06
       status: completed
-    - name: Netwerkupgrade: minimale ringgrootte verhogen naar 7, multisig integreren, subadressen, PoW-algoritme wijzigen
+    - name: "Netwerkupgrade: minimale ringgrootte verhogen naar 7, multisig integreren, subadressen, PoW-algoritme wijzigen"
       date: 2018-04-06
       status: completed
     - name: Getmonero.org vertaald in het Frans en Pools