MastodonApi: add support for subscribing endpoints and subscribing status field

app/src/main/java/com/keylesspalace/tusky/entity/Relationship.kt

@@ -24,5 +24,6 @@ data class Relationship (
     val blocking: Boolean,
     val muting: Boolean,
     val requested: Boolean,
-    @SerializedName("showing_reblogs") val showingReblogs: Boolean
+    @SerializedName("showing_reblogs") val showingReblogs: Boolean,
+    val subscribing: Boolean? = null // Pleroma extension
 )

app/src/main/java/com/keylesspalace/tusky/network/MastodonApi.kt

@@ -325,6 +325,16 @@ interface MastodonApi {
     fun identityProofs(
             @Path("id") accountId: String
     ): Call<List<IdentityProof>>
+    
+    @POST("api/v1/pleroma/accounts/{id}/subscribe")
+    fun subscribeAccount(
+        @Path("id") accountId: String
+    ): Call<Relationship>
+    
+    @POST("api/v1/pleroma/accounts/{id}/unsubscribe")
+    fun unsubscribeAccount(
+        @Path("id") accountId: String
+    ): Call<Relationship>
 
     @GET("api/v1/blocks")
     fun blocks(
@@ -498,6 +508,16 @@ interface MastodonApi {
     fun unmuteAccountObservable(
             @Path("id") accountId: String
     ): Single<Relationship>
+    
+    @POST("api/v1/pleroma/accounts/{id}/subscribe")
+    fun subscribeAccountObservable(
+        @Path("id") accountId: String
+    ): Single<Relationship>
+    
+    @POST("api/v1/pleroma/accounts/{id}/unsubscribe")
+    fun unsubscribeAccountObservable(
+        @Path("id") accountId: String
+    ): Single<Relationship>
 
     @GET("api/v1/accounts/relationships")
     fun relationshipsObservable(