Add billings module
Added temporary style-btn for later use.
Added salesinvoice module, edited file-button css
Merge branch 'master' of https://github.com/jbantug/meteorERP

Conflicts:
	client/client.html
	client/templates/template_billings.html
Added template_salesinvoice
Edited salesinvoice css module.
updated UI and added billing module
Merge branch 'master' of https://github.com/jbantug/meteorERP

Conflicts:
	client/client.html
	client/templates/template_billings.html