v0.29.0-beta release

Features:

• #356 custom request handlers
• custom CSS themes, added an example theme called Steel Blue into demo document.
• refactored consistency checks + more "auto fixers" for possible issues
• #385 URL to create a search

Bug fixes:

• #392 Better icon for iOS' homescreen
• #387 Fixed extra angle brackets in tree in dark themes
• #384 Character code specification in HTML header
• #377 add confirm type change dialog when note not empty
• #376 Alt-Left and Alt-Right Key Bindings for Mac
• #375 Moving sometimes has strange side effects