improve param handling

- the diff is now compatible with the parameters of version 0.2
- new method of linking is rewritten to be complatible with the changes
- add new button to bar: Link - brings up a window which tells you the
link to the current query displayed in the output

how linking works:
- single query (table and "show all" are same for all ids):
/diff/?m=<first letter of table, eg. q for quest template>&f=<show all
if on (optional)>&id=<a single id or more ids separated by commas>
(example: /diff/?m=q&f=on&id=256,257 or /diff/?m=q&f=on&id=257)

- multiple query (table and "show all" may differ among the ids):
/diff/?m=<always m>&id=<show all: 1 - true, 0 - false><first letter of
table><id>, <...>
(example: /diff/?m=m&id=1q256,0c21299,0i25)