Support couples - complex version

[danielabar]

Follow-on from #20 to improve accuracy of couples GIS amount:

Given that user has selected married or common-law as marital status, present two more input fields asking for current user's age and their spouse's current age. The differences in their respective ages matter when determining GIS because it guides which lookup table to use and for how many years. Lookup tables are as follows:

Table 1 - GIS for single, widowed or divorced person who receives an OAS pension
-> No spouse
Table 2 - Married or common-law OAS pensioner and spouse is also an OAS pensioner
-> Spouse is 65+
Table 3 - Married or common-law OAS pensioner and spouse is not an OAS pensioner
-> Spouse is below 60
Table 4 - Married or common-law OAS pensioner and spouse receives the Allowance
-> Spouse is 60 - 64

May need to re-think design of some charts, or make some assumptions that the Monthly and Annual charts represent first year of user receiving GIS.

Then for total lifetime of GIS chart, need to calculate "phases" as user and spouse go through the ages that would hit the different tables.