Move sidemenu css styles up to the sidebar styles global css file

Given this is css that is no longer specific to the sidemenu component
itself and is in itself to be used nested within an `.op-sidebar` element, it
makes sense to extract this out and make it globally available to other sections
of the application.

frontend/src/app/shared/components/sidemenu/sidemenu.component.ts

@@ -27,7 +27,6 @@ export const sidemenuSelector = 'op-sidemenu';
 @Component({
   selector: sidemenuSelector,
   templateUrl: './sidemenu.component.html',
-  styleUrls: ['./sidemenu.component.sass'],
   changeDetection: ChangeDetectionStrategy.OnPush,
 })
 export class OpSidemenuComponent {

frontend/src/global_styles/content/_sidebar.sass

@@ -23,4 +23,65 @@
     .button .spot-icon
       margin-right: 0.5rem
 
-@import 'app/shared/components/sidemenu/sidemenu.component'
+  .op-sidemenu
+    display: flex
+    flex-direction: column
+    font-size: 14px
+
+    &--title
+      display: flex
+      background: transparent
+      color: var(--main-menu-fieldset-header-color)
+      border: 0
+      text-transform: uppercase
+      padding: 8px 12px
+      margin-top: 12px
+      font-size: 12px
+      cursor: pointer
+
+      &.-spread
+        justify-content: space-between
+
+      &:hover
+        background: var(--main-menu-bg-hover-background)
+        color: var(--main-menu-hover-font-color)
+
+    &--items
+      list-style: none
+
+      &_collapsed
+        display: none
+
+    &--item-action
+      display: flex
+      align-items: center
+      color: var(--main-menu-font-color)
+      padding: 8px 12px 8px 32px
+
+      &:hover
+        background: var(--main-menu-bg-hover-background)
+        color: var(--main-menu-hover-font-color)
+
+      &_active
+        background: var(--main-menu-bg-selected-background)
+        color: var(--main-menu-selected-font-color)
+
+      &_active-child
+        background: var(--main-menu-bg-selected-background)
+        color: var(--main-menu-selected-font-color)
+
+      &_with_icon
+        padding-left: 12px
+
+    &--item-title
+      margin-right: auto
+      overflow: hidden
+      text-overflow: ellipsis
+      white-space: nowrap
+      line-height: 30px
+      text-decoration: none
+      width: 100%
+
+    &--item-icon
+      font-size: 24px
+      margin-right: 8px