Show genres tab for TV & Movies (#16)

Adds a tab to the TV Show & Movie screens which displays the genres in
that library as a grid.

You can select the genre to see the items in that library for the genre.

This PR also adds backend changes for further filtering to implement
#13.

app/src/main/java/com/github/damontecres/wholphin/data/model/GetItemsFilter.kt

@@ -0,0 +1,31 @@
+@file:UseSerializers(UuidSerializer::class)
+
+package com.github.damontecres.wholphin.data.model
+
+import com.github.damontecres.wholphin.util.UuidSerializer
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.UseSerializers
+import org.jellyfin.sdk.model.api.request.GetItemsRequest
+import java.util.UUID
+
+@Serializable
+data class GetItemsFilter(
+    val favorite: Boolean? = null,
+    val genres: List<UUID>? = null,
+    val minCriticRating: Double? = null,
+    val persons: List<UUID>? = null,
+    val played: Boolean? = null,
+    val studios: List<UUID>? = null,
+    val tags: List<String>? = null,
+) {
+    fun applyTo(req: GetItemsRequest) =
+        req.copy(
+            isFavorite = favorite,
+            genreIds = genres,
+            minCriticRating = minCriticRating,
+            personIds = persons,
+            isPlayed = played,
+            studioIds = studios,
+            tags = tags,
+        )
+}