Added import function for html-files/webpages. The function can 
	- import a html-file
	- import a folder full of html-files (so long as they have the same
html-structure)
	- import a webpage
	- import a .txt-file with a list of links (so long as they come from
the same webpage with the same html-structure).

Open tasks: 
Date Extractor: 

TODO: Warning "date not extractable. Choose 'set date manually'-option"
TODO: How to handle am/pm when setting hh:mm
TODO: Support different locales

ImportHTML/ImportWebpage:  

TODO: Add buffering-symbol when importing documents
TODO: get icon with document and magnifying glass
TODO: Warning "no internet connection"

Generally: 

TODO: extensive tests w/different html-files/webpages
TODO: ask selectorGadget for permission to use link to tool (?)