Custom error for access to deleted post

Added custom error triggered by find_comment_id() to make difference between deleted post and nonexisting one. All API calls that use this SQL function are affected (unfortunately it is not yet used everywhere).

get_content/get_content_replies reimplemented as SQL functions

removed superfluous code from condenser_api

restored mute handling in get_content_replies for consistency with get_content

hive/db/sql_scripts/condenser_api_post_ex_type.sql

+DROP TYPE IF EXISTS condenser_api_post_ex CASCADE;
+-- type for fat node style post of get_content()
+CREATE TYPE condenser_api_post_ex AS (
+    id INT,
+    author VARCHAR(16),
+    permlink VARCHAR(255),
+    author_rep BIGINT,
+    title VARCHAR(512),
+    body TEXT,
+    category VARCHAR(255),
+    depth SMALLINT,
+    promoted DECIMAL(10,3),
+    payout DECIMAL(10,3),
+    pending_payout DECIMAL(10,3),
+    payout_at TIMESTAMP,
+    is_paidout BOOLEAN,
+    children INT,
+    votes INT,
+    created_at TIMESTAMP,
+    updated_at TIMESTAMP,
+    rshares NUMERIC,
+    abs_rshares NUMERIC,
+    json TEXT,
+    is_hidden BOOLEAN,
+    is_grayed BOOLEAN,
+    total_votes BIGINT,
+    net_votes BIGINT,
+    total_vote_weight NUMERIC,
+    parent_author VARCHAR(16),
+    parent_permlink_or_category VARCHAR(255),
+    curator_payout_value VARCHAR(30),
+    root_author VARCHAR(16),
+    root_permlink VARCHAR(255),
+    max_accepted_payout VARCHAR(30),
+    percent_hbd INT,
+    allow_replies BOOLEAN,
+    allow_votes BOOLEAN,
+    allow_curation_rewards BOOLEAN,
+    beneficiaries JSON,
+    url TEXT,
+    root_title VARCHAR(512),
+    active TIMESTAMP,
+    author_rewards BIGINT
+);