feature: initial support month-picker support

https://github.com/danielmoncada/date-time-picker/issues/94

Via the property 'yearOnly'

<input [(ngModel)]="selectedMoments" [selectMode]="'range'"
       [owlDateTimeTrigger]="date_range_component" [owlDateTime]="date_range_component"
       style="width: 100%; color: cornflowerblue"
       id="daterange" matInput required>

<owl-date-time #date_range_component [startAt]="currentValue" startView="year" [yearOnly]="true" [endAt]="endValue"
(monthSelected)="startMonthHandler($event, selectedMoments)">
</owl-date-time>

danielmoncada / date-time-picker

feature: initial support month-picker support #95