fix: minor changes and fixes to Payments

[18alantom]

• Handle "Saving..." hang up.
• Prevent altering Submitted submittable doctypes (such as Payments) from the quick view.
• Add reversion and ledger link to Payment quick form view.
• Rename Payment For to Payment References. (∵ the field name shows on error and "Payment For" doesn't show any where, table column names have "Reference" in them so this is less confusing)
• Make for not mandatory. (∵ deferred to ERPNext functionality)
• Allow any amount to be set if no reference. (∵ used to set to 0 otherwise)
• Ref. / Cheque No. is mandatory only if method is not Cash. (∵ Cash Payments may not have a reference)
• Add migration for the Payment table. (∵ changes in for and referenceId changes) Added this as an exercise.
• Convert default calling Date to functional defaults. (∵ Default gets set whenever the script is done so table updates sets defaults )
• Formatting fixes.

Note: SQLite doesn't allow column changes, so table will have to be prestiged even for minor changes like flipping a NOT NULL.

(fixes boolean from previous PR, didn't realize this got added in)

Fixes: #137 #178

Needs frappejs/pull/152 to work.