Exclude files that user is not allowed to download

Based on the type of ecoinvent license, not all files are actually
available to download even though they're listed in the page source.
Files with the html class 'fileDownloadNotAllowed' are now excluded.

eidl/core.py

@@ -97,9 +97,11 @@ def get_available_files(self):
             self.handle_connection_timeout()
             raise e
         soup = bs4.BeautifulSoup(files_res.text, 'html.parser')
-        file_list = [l for l in soup.find_all('a', href=True) if
+        all_files = [l for l in soup.find_all('a', href=True) if
                      l['href'].startswith('/File/File?')]
-        link_dict = {f.contents[0]: f['href'] for f in file_list}
+        not_allowed = soup.find_all('a',  class_='fileDownloadNotAllowed')
+        available_files = set(all_files).difference(set(not_allowed))
+        link_dict = {f.contents[0]: f['href'] for f in available_files}
         link_dict = {
             k.replace('-', ''):v for k, v in link_dict.items() if k.startswith('ecoinvent ') and
             k.endswith('ecoSpold02.7z') and not 'lc' in k.lower()