Message template variables: improve consistency of variables & testing and add financialTypes

I have 2 issues in here

1) improve the standardisation of values between different message templates. In general I find most sites would prefer to use the same template for front end and back office forms and the inconsistency of variables is an issue. I have added an assignment of {$amount} to back office contribution form to match front office and added comments

2) Lack of visibility of the 'actual' financial types in the line items is an issue. I have added 2 new variables:

{$financialTypes} (e.g 'Donation' for a single line item or all line items of the same type, or 'Donation|Sales Tax|Member Fee' for a more complex purchase)

{$financialTypeArray} - this is the same as above but assigned as a keyed array. The former is more likely to be useful for printing. The latter for iterating through in an IF

I have dithered backwards & forwards on the former between comma & pipe as a separator - after typing it I lean back to comma  since I mostly imagine in being used for display.

We already have $financialType & $contributionType used somewhat inconsistently. The issue is that refers to the type of contribution record and that often has no relation to what people have actually selected.