v0.3.0

This release includes the following changes:

• the composer is now hidden in rooms where you don't have permission to write (#788)
• the /join command was added, thanks to @Kaki-In! (#809)
• the last location is now restored again when opening the app, thanks to @Kaki-In. (#816)
• room keys are now shared according to the room history visibility, for example with invited members where appropriate (#811)
• runtime themes are now supported, you can now change the colors (including the icons!) of one of the built-in themes with just a json file, no rebuild needed! See the docs for more info (#769)

In addition to this, we've converted some parts of the code to typescript (#676, #777 thanks to @ibeckermayer!) and we've improved the documentation (#813, #812, #758, #752 and #778).