GitRepository: added getRepositoryPath() method.

Signed-off-by: Jan Pecha <janpecha@email.cz>
GitRepository: added static init() method

Signed-off-by: Jan Pecha <janpecha@email.cz>
GitRepository: updated init()

Signed-off-by: Jan Pecha <janpecha@email.cz>
composer.json: updated description

Signed-off-by: Jan Pecha <janpecha@email.cz>
required Nette\Tester for tests

Signed-off-by: Jan Pecha <janpecha@email.cz>
GitRepository: used exec() instead of system()

Signed-off-by: Jan Pecha <janpecha@email.cz>
Tests: added basic test

Signed-off-by: Jan Pecha <janpecha@email.cz>