Update vars descriptions

[inikolova]

https://github.com/telerik/kendo-themes-private/issues/92

Note: Some of the components listed in the issue above don't have dedicated folders with variables and styles -> they rely on the styles of other components. Below is a list with them:

• MultiSelectTree - uses the styles for input, button, chip, popup, treeview;
• DateInput - uses the styles for k-input;
• ChipList - uses the styles for the chip. Its specific variables are only for the sizes -> https://github.com/telerik/kendo-themes/blob/develop/packages/default/scss/chip/_variables.scss#L173
• ColorPicker - uses the styles for the colorEditor;
• FlatColorPicker - uses the styles for the colorEditor;
• MultiColumnComboBox - uses the styles for input, button, popup, data table;
• SearchBox - uses the styles for the input;

CheckboxGroup and RadioButtonGroup variables have been documented with these commits:

• CheckboxGroup - c2bd9d8#diff-4fa806c700a6f99c7de8355c97b6bf7252345d54803cbbfed7a83315b5bb6f4bR174

• RadioButtonGroup - c2bd9d8#diff-762fcabdeabea89ff3a9cf344907886b611cc1bed8614c356698d18d56bea3ccR166

[yordan-mitev]

The changes look good. I made some minor changes in the variable descriptions and in some of the component names for the Default theme. You can propagate them to the rest of the themes as well.