refactor: Restructure account slip structure

[sfount]

Currently the account slip is used to show detailed information on transactions that have hit an account. It is very similar as the 'Account Report'. I suggest that we restructure these reports to minimise the amount of code to be maintained and simplify future development.

File structure:

• Move account slip under the accounts report folder so that it can be found at finance/reports/accounts/slip
• Separate the account slip code from the general ledger controller so that it can be found at finance/reports/accounts/slip.js

UX structure:

• Use the exact same template/ controller for both the report and the slip that can be displayed within modules
• Allow easy filtering of the slip to only show data from a specific time period

Report logic:

• Use MySQL or well defined JavaScript to calculate totals so that the template is not responsible for this - contributes to (chore) Remove helpers/math.js #1668
• Separate getAccountTransactions from the reportAccounts.js controller so that it can be used by other services/ controllers

[jniles]

I'll tackle this in my General Ledger refactor (#2462). The account report has evolved quite a bit, so this will probably link directly to the account report for the selected FY.