Write unittests for the ReleaseCandidateScraper Class

[Nebelhom]

Implement all the current manual tests for the ReleaseCandidateScraper class and then remove them from the list of manual test cases. At the moment, these are:

Firefox

mozdownload -t candidate -p win32 -v 21.0
mozdownload -a firefox -t candidate -p linux -v 21.0
mozdownload -a firefox -t candidate -p linux64 -v 21.0
mozdownload -a firefox -t candidate -p mac -v 21.0
mozdownload -a firefox -t candidate -p win32 -v 21.0
mozdownload -a firefox -t candidate -p win32 -v 21.0 -d firefox-candidate-builds
mozdownload -a firefox -t candidate -p win32 -v 21.0 -l cs
mozdownload -a firefox -t candidate -p win32 -v 21.0 -l en-GB
mozdownload -a firefox -t candidate -p win32 -v 21.0 --build-number=1
mozdownload -a firefox -t candidate -p win32 -v 21.0 --stub

Thunderbird

mozdownload -a thunderbird -t candidate -p linux -v 10.0.5esr
mozdownload -a thunderbird -t candidate -p linux64 -v 10.0.5esr
mozdownload -a thunderbird -t candidate -p mac -v 10.0.5esr
mozdownload -a thunderbird -t candidate -p win32 -v 10.0.5esr
mozdownload -a thunderbird -t candidate -p win32 -v 10.0.5esr -d thunderbird-candidate-builds
mozdownload -a thunderbird -t candidate -p win32 -v 10.0.5esr -l cs
mozdownload -a thunderbird -t candidate -p win32 -v 10.0.5esr -l en-GB
mozdownload -a thunderbird -t candidate -p win32 -v 10.0.5esr --build-number=1

[whimboo]

Those tests have been landed via pull #165. Thanks @Nebelhom!