refactor(theme): remove angular2-toaster styling (#721)

BREAKING CHANGE:
angular2-toaster styles were removed from Nebular.
Instead, we suggest using our new `NbToastrService`.

To Update:
Add `NbToastrModule` into imports of your `app.module`.
Inject `NbToastrService` into the required component.
call `NbToastrService.show(...)` to render toasts.
For more information check [toastr documentation](https://akveo.github.io/nebular/docs/components/toastr).

docs/articles/concept-3rd-party.md

@@ -3,32 +3,11 @@
 Currently Nebular Theme system is integrated with the following 3rd party modules:
 
 - ng2-smart-table;
-- angular2-toaster.
 
 It means that we've created style overriding for these modules, so that you can change component's look & feel using Nebular theme variables.
 For example, if you change the `color-primary` variable, components using this color will be changed accordingly.
 
-
-Or that's how we described variables for the `angular2-toaster` module:
-
-```scss
- ...
- toaster-bg: color-primary,
- toaster-fg-default: color-inverse,
- toaster-btn-close-bg: transparent,
- toaster-btn-close-fg: toaster-fg-default,
- toaster-shadow: shadow,
-
- toaster-fg: color-white,
- toaster-success: color-success,
- toaster-info: color-info,
- toaster-warning: color-warning,
- toaster-wait: color-primary,
- toaster-error: color-danger,
- ...
-
-```
- <hr>
+<hr>
 
 ## Related Articles
 

src/framework/theme/components/toastr/_toast.component.theme.scss

@@ -4,7 +4,7 @@
  * Licensed under the MIT License. See License.txt in the project root for license information.
  */
 
-@mixin nb-toaster-theme() {
+@mixin nb-toast-theme() {
  nb-toast {
  background-color: nb-theme(toastr-bg);
  padding: nb-theme(toastr-padding);

src/framework/theme/styles/global/_components.scss

@@ -66,7 +66,7 @@
  @include nb-popover-theme();
  @include nb-context-menu-theme();
  @include nb-select-theme();
- @include nb-toaster-theme();
+ @include nb-toast-theme();
  @include nb-tooltip-theme();
  @include nb-window-theme();
 }

src/framework/theme/styles/global/_overrides.scss

@@ -6,7 +6,6 @@
 
 @import 'normalize.scss';
 @import 'components/tree.theme';
-@import 'components/toaster.theme';
 @import 'maps/leaflet.theme';
 @import 'tables/smart-table.theme';
 
@@ -17,5 +16,4 @@
  @include nb-components-tree-theme();
  @include nb-maps-leaflet-theme();
  @include nb-tables-smart-table-theme();
- @include nb-components-toaster-theme();
 }

src/framework/theme/styles/themes/_default.scss

@@ -302,19 +302,6 @@ $theme: (
  smart-table-paging-bg-active: color-success,
  smart-table-paging-hover: rgba(0, 0, 0, 0.05),
 
- toaster-bg: color-primary,
- toaster-fg-default: color-inverse,
- toaster-btn-close-bg: transparent,
- toaster-btn-close-fg: toaster-fg-default,
- toaster-shadow: shadow,
-
- toaster-fg: color-white,
- toaster-success: color-success,
- toaster-info: color-info,
- toaster-warning: color-warning,
- toaster-wait: color-primary,
- toaster-error: color-danger,
-
  toastr-bg: color-bg,
  toastr-padding: 1.125rem,
  toastr-fg: color-fg-text,