Great linting fixes has been applied, thanks to golangci-lint for
extensive reporting.
Fixed Drone configuration to use array for when-branch statement in
Docker plugin.
Flatfile storage from now will write files with 0600 permission for
greater security.
Added forgotten dependencies update.
Fixed fastpastebin crash when database isn't available and added cute
error screen for informing users about such condition (both HTML and raw).
Added captcha generation. As we're working without JS - there is no
possibility to reload image, only if user will reload whole web page.
Some design works - set monospace font for paste textarea (will
use system-defined default monospace font) and lowered font size
in paste views.
