Multiple Link Previews

- Show a preview for each link in the text below the block in which it appears.
- Allow link previews to be dismissed

autotests/data/test-invalidmatrixtolink-event.json

@@ -1,14 +0,0 @@
-{
-    "content": {
-        "body": "https://matrix.to/#/@alice:example.org",
-        "msgtype": "m.text"
-    },
-    "event_id": "$validlink1:example.org",
-    "origin_server_ts": 1432735824654,
-    "room_id": "!test:example.org",
-    "sender": "@example:example.org",
-    "type": "m.room.message",
-    "unsigned": {
-        "age": 1234
-    }
-}

autotests/data/test-invalidmxclink-event.json

@@ -1,14 +0,0 @@
-{
-    "content": {
-        "body": "mxc://example.org/SEsfnsuifSDFSSEF",
-        "msgtype": "m.text"
-    },
-    "event_id": "$validlink1:example.org",
-    "origin_server_ts": 1432735824654,
-    "room_id": "!test:example.org",
-    "sender": "@example:example.org",
-    "type": "m.room.message",
-    "unsigned": {
-        "age": 1234
-    }
-}

autotests/data/test-invalidnospacelink-event.json

@@ -1,14 +0,0 @@
-{
-    "content": {
-        "body": "testhttps://kde.org",
-        "msgtype": "m.text"
-    },
-    "event_id": "$validlink1:example.org",
-    "origin_server_ts": 1432735824654,
-    "room_id": "!test:example.org",
-    "sender": "@example:example.org",
-    "type": "m.room.message",
-    "unsigned": {
-        "age": 1234
-    }
-}

autotests/data/test-validplainlink-event.json

@@ -1,14 +0,0 @@
-{
-    "content": {
-        "body": "https://kde.org",
-        "msgtype": "m.text"
-    },
-    "event_id": "$validlink1:example.org",
-    "origin_server_ts": 1432735824654,
-    "room_id": "!test:example.org",
-    "sender": "@example:example.org",
-    "type": "m.room.message",
-    "unsigned": {
-        "age": 1234
-    }
-}

autotests/data/test-validplainwwwlink-event.json

@@ -1,14 +0,0 @@
-{
-    "content": {
-        "body": "www.example.org",
-        "msgtype": "m.text"
-    },
-    "event_id": "$validlink1:example.org",
-    "origin_server_ts": 1432735824654,
-    "room_id": "!test:example.org",
-    "sender": "@example:example.org",
-    "type": "m.room.message",
-    "unsigned": {
-        "age": 1234
-    }
-}

autotests/data/test-validrichlink-event.json

@@ -1,16 +0,0 @@
-{
-    "content": {
-        "body": "[Rich Link](https://kde.org)",
-        "format": "org.matrix.custom.html",
-        "formatted_body": "<a href=\"https://kde.org\">Rich Link</a>",
-        "msgtype": "m.text"
-    },
-    "event_id": "$validlink1:example.org",
-    "origin_server_ts": 1432735824654,
-    "room_id": "!test:example.org",
-    "sender": "@example:example.org",
-    "type": "m.room.message",
-    "unsigned": {
-        "age": 1234
-    }
-}