Rename QML module import name

For SailfishOS, rename to "harbour.quickddit.Core" (Jolla Harbour
requirement). For Harmattan, rename to "Quickddit.Core".
Rearrange toolbar/pull down menu in MainPage

* (Sailfish) Add a "More" item in PullDownMenu, items that are not
relevant to current context are move inside
* (Harmattan) Rearrange toolbar and menu items to consistent with
Sailfish version
Update AboutPage
Fix falsely showing the user as the submitter

When posting comment on other user's post
Add multireddits support
Add convenient functions in QuickdditManager.cpp

For reduce number of #if #else for Qt4/5 and makes the code looks nicer
New feature: (Private) Message
Improve VoteManager

Remove "type" and "model" property. When vote success, it will emit a
voteSuccess signal and QML will execute LinkModel/CommentModel
changeLikes(), instead of execute in C++ by VoteManager. This make
VoteManager works more independently and remove dependency on
LinkModel/CommentModel.
CommentPage can load the LinkObject by itself

Previously CommentPage is depends on the LinkModel to get the link
object. This causes the CommentPage can not be push to pageStack outside
LinkModel. Now when the link object is not provided by the LinkModel
(pushed to pageStack outside a LinkModel) CommentModel will parse the
LinkObject from the comments response and expose to QML (by converting
to a QVariantMap). This allow pushing CommentPage to pageStack while in
MessagePage.
Show a text and view all comments button when viewing a single comment
Add reply, mark read and mark unread functions to message
Fix for sent message

Show the recipient instead of author and disable reply and mark as
read/unread functions for sent message
Improve load more button/menu

Set the visibility of load more button/menu to false when there is no
more item can be loaded
(Sailfish) Use BusyIndicator instead of ProgressCircle
Fix some characters are not encoded when sending request

Encode query string manually because QUrl::addQueryItem() does not
encode some of the characters (eg. colon and semi colon)