Bootstrap variables

To improve the writing of a custom SCSS code in our package, from the MDB 4.5.2 version, there are three new files available, in which you can place various variables.

In the _custom-variables.scss you can add variables with the same names as ours and you want to overwrite them.

In the _custom-skin.scss you can add an object with values to create your custom skin.

In the _custom-styles.scss you can add all other styles.