Application Cache Changes

[StuartFerguson]

Review use of application cache

Main requirements for the cache are as follows:

1. cache access token from auth service until it expires and get a new token then it has expired
2. Cache the app configuration from the config service call, if this is requested at any point and has expired this must be re-pulled from the config service
3. Cache merchant information for a period and if this is requested at any point and has expired this must be re-pulled from the merchant service
4. Cache contract/product information for a period and if this is requested at any point and has expired this must be re-pulled from the merchant service

What i cant decide is the expiry times for 2,3 and 4

I also want to have my merchant balance cached so this can be displayed on the front screen somewhere, this will be managed by the balance refresher