Fix GUI limit issue for "Packs" and "Triggers" (cf. `st2web` issue #1034).

[TimothyDJones]

Increase default for `limit` parameter to 500.

Default is increased for `packs` and `triggertypes` to fix
GUI problem with "panel" lists for "Packs" and "Triggers"
not displaying complete data due to current limit of 100,
when many packs and/or triggers are registered in ST2.

Update fixes `st2web` issue #1034.
https://github.com/StackStorm/st2web/issues/1034

[fdrab]

isn't this a configurable parameter in the configs?

# Maximum limit (page size) argument which can be specified by the user in a query string.
max_page_size = 100