dict: improve overriding of default server and dictionary

runners/dict and applets/dict use DictEngine to query for words. The default server and dictionary can be overridden by passing them as part of the query itself. For example to use dict.myserver.com as server and wn for dictionary:

• To override dictionary in runners/dict: define wn:hello
• To override server and dictionary in runners/dict: define dict.myserver.com:wn:hello
• To override server and dictionary in applets/dict: dict.myserver.com:wn:hello

The query is passed to DictEngine::requestDefinition where the engine sets the server and dictionary.

Problems

• This is a hard to use feature as the end user is expected to know the server name and dictionary. I think very few users even know about this.
• If the applet or runner making use of DictEngine::requestDefinition want to override the default server they are also forced to pass the dictionary name.

Solution

• Dropped the existing functionality of specifying server and dictionary in the query to override the defaults.
• Overloaded DictEngine::requestDefinition to allow overriding of dictionary, server or both.

Changes to applets/dict

• Now definition is requested using requestDefinition(query, dictionary) instead of passing the dictionary in the query itself.
• Users won't be able to override server and dictionary from the query itself like dict.myserver.com:wn:hello but they can still directly search the word.

Changes to runners/dict

• Users won't be able to override server and dictionary from the query itself like define wn:hello or define dict.myserver.com:wn:hello but they can still do define hello.

Note

- This would break applets/dict. I plan to make a follow up MR to fix it. The fix to applets/dict has been added to this MR itself.