refractor(theme): set the theme from login and update default theme to (#128)

denim-yellowgreen

Set the theme from the login page itself if present in local storage and
update default theme to denim-yellowgreen (based on logo of Mifos).

Fixes #127

src/main.scss

@@ -4,7 +4,7 @@
  */
 
 // Import Default Theme for MifosX
-@import "~@angular/material/prebuilt-themes/indigo-pink.css";
+@import "theme/custom/denim-yellowgreen";
 
 // 3rd party libraries