Handle custom limit in query parameter

[MattiasSp]

Fixes #110.

Related to origo-map/origo#1413 and origo-map/origo#1418.

The limit on the number of search hits returned now follows the same behaviour in the following handlers:

• search.js
• searchaddressestate.js
• singlesearch.js

The maximum number of hits returned by Origo Server is controlled solely in dbconfig.js. A more specific limit will take precedence over a more general limit:
module.exports.models.search.search.tables[0].limit > module.exports.models.search.search.limit > module.exports.limit

If the request url includes the new &limit={max no of hits} parameter, this parameter's value will be used only if it is lower than that set in dbconfig.js.

If there is no limit set at all, either in dbconfig.js or as a url parameter, then 100 hits is the maximum (same as before).

A special note: I added limit handling for the oracledefault.js db model to make it behave similarly to pgdefault.js and mssqldefault.js. I also removed the limit parameters that was being sent to the db models.

• It was only used in pg and mssql (so not consistent)
• There was duplication of logic
• There were default values (1000) that could never be assigned (since the value had 100 set both in dbconfig.js and in the handlers

[MattiasSp]

FYI regarding the failed test: the warnings are about problems in the file routes/mapstate.js, which this PR doesn't touch. So I think it should be disregarded and those problems should be fixed in a separate PR.