Updating NuGet reference and adding Aria doenloader

Updating NuGet reference to 2.8.2 and adding classes to support
downloading NuGet packages using aria2c  command

Improving AriaDownloader

Adding parameters to aria downloader:
MaxConnections,
LogFilePath,
LogSeverity,

makes all arguments accessible from app.config file

Refactoring AriaDownloader and FileWrier

Chanfing FilesPaths var to FilesPath and arranging AriaDownloaderCode to
download the files in the Download method

Logging files & add Log4Net Package

Add logging to the following files:
Program,
AriaDownloader,
FileWriter

Refactoring FileWriter

Fixing typo and changing log line

Adding Unit Tests for FileWriter

Covering all cases in FileWriter & fixing the FileWriter according to
the UnitTests.

Comments for the Tests are still required (maybe next Check In :)

Moving the IsPathValid from AriaDownloader To HelperMethods

Adding AriaDownloaderTests

Adding test and Intergration tests,
Fixing problems in Filewriter and AriaDownloader according to the Unit
tests

Documenting and rearrange the Unit Tests

Getting the NuGet url from configuration

Adding async await where necessary

Improving the main program

1. downloading packages from the last time the program was activated and
saving the new time in the configuration file
2. Fixing the value of LoggerFileName in the configuration
3. logging unhandleexception

Fixing Bugs in AriaDownloader

1. Coping aria2c.exe to OutputDirectory
2. fixing argument bug in AriaDownloader
3. Making FileWriter sync (and removing async from the test files.
3. Updating NugetDownloader to replace the original NuGet url

Removing unnecessary Aria log creating

It appears that aria2c.exe creates the log itself if it detects the log
does not exist so it redundent to create it

Chaning the configuration

1. Adding IshimottoConfig section
2. Removing the Settings annoing file
3. Removing redundent setting from app.config
4. Fixing bug - updating the LastFetchTime
5. Removing unnecessary methods
6. Setting NuGet Querier to take only he lastest version
Code refactor
Merge pull request #2 from darkl/aria2

Add changes made by @TMaster, with some refactor.