Take a picture as attachment in-app

New feature: take a picure within Whisperfish and send it as an attachment. The UI isn't pretty, but the basic functionality works, so feel free to try it out!

The important stuff:

• Save the picture in Whisperfish storage path
• Handle device rotation (very slightly janky, but works great)
• Add the picture as an attachment and send it!
• Tap to focus
• Create dedicated folder for pics under storage (needs a new QSetting key and related Rust code)
• Delete the taken picture, if user rejects it (needs Rust code?)
• Re-arrange the attachment buttons in ChatTextInput.qml (they take up too much space as-is)

Postponed:

• Make the UI prettier
• Auto-focus (unless tapped-to-focus)
• Video (should be easy, but practically requires delete-rejected functionality)
• Use front camera (easy, but needs new tedious orientation hunt)
• White balance, exposure, focus, flash controls (at least some subset of these)

Getting device orientation + UI orientation + viewfinder + photo orientation all work together was tricky, but it all works fine. Tested successfully with

• Sony Xperia X 10 II (4.4)
• Sony Xperia XA2 Ultra (4.4)
• Sony Xperia X (4.1)
• Jolla Phone (3.4)

Fixes #7 (closed)