prepare release of v3.0.0

bump up version number for release

Fix CSS font settings

'error' make this message more prominent (even though it is technical…

…ly just an information)

more concise text in export dialog

disable new feature 'import from URL' for v2.1.0

disable new feature for patch release v2.0.1

release v2.0.0

release-prepare

Version bump for release 1.4.0