Add YAML-metadata for notes and change the document title accordingly (#310)

* Added yaml-frontmatter extracting and error handling
* add tests
* changed document-title, so the editor can change the title to the title of the yaml metadata. closes #303
* extracted first line parsing in a core rule of markdown-it
document title will now be determined like this:
1. yaml metadata title
2. opengraph title
3. first level one heading
4. 'Untitled'
* added documentTitle e2e test

Co-authored-by: Erik Michelson <github@erik.michelson.eu>
Co-authored-by: Philip Molares <philip@mauricedoepke.de>
Co-authored-by: Tilman Vatteroth <tilman.vatteroth@tu-dortmund.de>
Co-authored-by: mrdrogdrog <mr.drogdrog@gmail.com>

cypress/integration/documentTitle.spec.ts

@@ -0,0 +1,67 @@
+import { branding } from '../support/config'
+
+const title = 'This is a test title'
+describe('Document Title', () => {
+  beforeEach(() => {
+    cy.visit('/n/test')
+    cy.get('.btn.active.btn-outline-secondary > i.fa-columns')
+      .should('exist')
+    cy.get('.CodeMirror textarea')
+      .type('{ctrl}a', { force: true })
+      .type('{backspace}')
+  })
+
+  describe('title should be yaml metadata title', () => {
+    it('just yaml metadata title', () => {
+      cy.get('.CodeMirror textarea')
+        .type(`---\ntitle: ${title}\n---`)
+      cy.title().should('eq', `${title} - CodiMD @ ${branding.name}`)
+    })
+
+    it('yaml metadata title and opengraph title', () => {
+      cy.get('.CodeMirror textarea')
+        .type(`---\ntitle: ${title}\nopengraph:\n  title: False title\n{backspace}{backspace}---`)
+      cy.title().should('eq', `${title} - CodiMD @ ${branding.name}`)
+    })
+
+    it('yaml metadata title, opengraph title and first heading', () => {
+      cy.get('.CodeMirror textarea')
+        .type(`---\ntitle: ${title}\nopengraph:\n  title: False title\n{backspace}{backspace}---\n# a first title`)
+      cy.title().should('eq', `${title} - CodiMD @ ${branding.name}`)
+    })
+  })
+
+  describe('title should be opengraph title', () => {
+    it('just opengraph title', () => {
+      cy.get('.CodeMirror textarea')
+        .type(`---\nopengraph:\n  title: ${title}\n{backspace}{backspace}---`)
+      cy.title().should('eq', `${title} - CodiMD @ ${branding.name}`)
+    })
+
+    it('opengraph title and first heading', () => {
+      cy.get('.CodeMirror textarea')
+        .type(`---\nopengraph:\n  title: ${title}\n{backspace}{backspace}---\n# a first title`)
+      cy.title().should('eq', `${title} - CodiMD @ ${branding.name}`)
+    })
+  })
+
+  describe('title should be first heading', () => {
+    it('just first heading', () => {
+      cy.get('.CodeMirror textarea')
+        .type(`# ${title}`)
+      cy.title().should('eq', `${title} - CodiMD @ ${branding.name}`)
+    })
+
+    it('just first heading with alt-text instead of image', () => {
+      cy.get('.CodeMirror textarea')
+        .type(`# ${title} ![abc](https://dummyimage.com/48)`)
+      cy.title().should('eq', `${title} abc - CodiMD @ ${branding.name}`)
+    })
+
+    it('just first heading without link syntax', () => {
+      cy.get('.CodeMirror textarea')
+        .type(`# ${title} [link](https://hedgedoc.org)`)
+      cy.title().should('eq', `${title} link - CodiMD @ ${branding.name}`)
+    })
+  })
+})