Fix progressive reveal and Topics with special characters not loading

[schloerke]

Fixes #320
Fixes #319

For #320, there was never a call to notify the js data model that the section had actually been skipped.

For #319, the hash was being returned as window.encodeURI output. By passing it through window.decodeURI, it behaves as expected.

File to test with

---
title: "learnr#330"
output:
  learnr::tutorial:
    progressive: true
    allow_skip: true
runtime: shiny_prerendered
---


## Section 1

### Subtopic 1

text

### Subtopic 2.

text

### Subtopic 3

text

## Säction title

### Subtopic 4

text

### Subtopic 5.

text

### Subtopic 6

text

• Should be able to click continue and also view the second section.