Code refactoring.

I've changed quite a lot internally. You can check out the last ~75 commits. Most of them were code refactoring and code enhancements. Should be mostly bugfree now.

New features are:

• Resumes incomplete downloads.
• Fixes incomplete video download.
• Downloader now stops immediately when stopping as downloads are resumable.
• Saves application settings now as json instead of xml. So you have to reset everything in the settings.
• The preview doesn't lag anymore and does not stall the application.
• It's now possible to drag&drop blogs from the manager (left) to the queue.
• An option to check the directory for already download files besides the internal database (#44).
• An option to download an url list instead of the actual binary files (#42).
• Fixes application crash if a drag&drop was initiated during a cell edit (e.g. tags cell) (#66).
• An application update checker.
• Downloads liked photos and videos, see #74 for more. For downloading those, you have to do some steps:
  1. Go to Settings, click the Authenticate button. Logon to tumblr using an account. The window/browser should automatically close after the login indicating a successful authentication. TumblThree will use the Internet Explorer cookies for authentication.
  2. Add the blog url including the liked/by string in the url (e.g. https://www.tumblr.com/liked/by/wallpaperfx/).
• Allows to change the visibility of the columns in the manager. There is a bug right now where you have to remove and re-add a column to display previously removed columns again.
• Adds a portable mode which stores the application settings next to the executable instead in the AppData folder.
• Fixes bandwidth throttling. Also allows to completely bypass it by setting the value to 0 in the settings.
• Allows to set proxy credentials (ProxyUsername, ProxyPassword) in plaintext in the settings file. Not tested.

Bugfixes:

• Fixes UI stall if many blogs were added using the ClipboardManager (#18).
• Fixes the autodownload function. Previously the stored value in the Settings.xml was used, not the one currently set (#63).

Bufixes since the first code refactoring (v1.0.4.31) release include:

• Fixes downloading of tagged files.
• Fixes application crash if a blog is added that is empty (#40).
• Fixes possible downloader stall (#75).
• Improves the photo and video detection in the tumblr likedby downloader (#77).

Note: If you have old binary data files (.tumblr) without the separated file list (_files.tumblr) you need to convert the big files into two smaller ones using the v1.0.4.31 release. After that you can use any of the newer releases.