[For 10.0.9] Template Editor 0.3.1 release

[PVince81]

Reason

• Release needed for Add activity html template support #69, [improvement] Implement best practices in code #70, Add footer template to editable list #71, Add notification email templates to editable list #73, mostly new editable templates

QA

• Create release branch @davitol https://github.com/owncloud/templateeditor/tree/release-0.3.1
• Create "$version Testplan" @davitol Tracking results for Template Editor v.0.3.1 #78
• Test and document in testplan => Final "Go" from QA (set 'QA-ready' label) @davitol

Marketing

• Ping RocketChat channel #marketing - skipped ( @patrickjahns )
• Check/adapt info.xml stuff - skipped ( @patrickjahns )
• Check/adapt screenshot - skipped ( @patrickjahns )
• Blog post or other communication if applicable

Documentation

• Changes in the docs needed?

Build & Marketplace release

• Bump version in info.xml - done via Update version and changelog for 0.3.1 #80
• Update CHANGELOG.md - Change CHANGELOG.md 'Unreleased' to '$version' done via Update version and changelog for 0.3.1 #80
• Create github tag for '$version' @patrickjahns
• Build and sign tarball from github tag '$version' @patrickjahns
• Upload to marketplace @patrickjahns
• Send mail to release-coordination with link to this ticket and to the changelog @patrickjahns
• Rename QA milestone to '$version' @patrickjahns
• Add a new 'Unreleased' section in CHANGELOG.md @patrickjahns
• Create PR to merge changes back to master @patrickjahns Release 0.3.1 #82

Specifics

• Open tickets before QA can start
• Other specifics for app release

[PVince81]

PR for changelog: #77