Use DownloaderImpl in CheckForNewAppVersionTask

[wb9688]

This way we only have to change code in DownloadImpl and the ExoPlayer stuff when we want to add support for e.g. setting a SOCKS proxy in the settings. I tested that this works successfully.

[TobiGr]

Could you also reduce this to one case:

NewPipe/app/src/main/java/org/schabi/newpipe/CheckForNewAppVersionTask.java

Lines 96 to 104 in 41061d0

	} catch (NoSuchAlgorithmException ex1) {
	ErrorActivity.reportError(APP, ex1, null, null,
	ErrorActivity.ErrorInfo.make(UserAction.SOMETHING_ELSE, "none",
	"Could not retrieve SHA1 key", R.string.app_ui_crash));
	} catch (CertificateEncodingException ex2) {
	ErrorActivity.reportError(APP, ex2, null, null,
	ErrorActivity.ErrorInfo.make(UserAction.SOMETHING_ELSE, "none",
	"Could not retrieve SHA1 key", R.string.app_ui_crash));
	}

        } catch (NoSuchAlgorithmException | CertificateEncodingException ex) {
            ErrorActivity.reportError(APP, ex, null, null,
                    ErrorActivity.ErrorInfo.make(UserAction.SOMETHING_ELSE, "none",
                            "Could not retrieve SHA1 key", R.string.app_ui_crash));
        }

[TobiGr]

One small thing