Fix header parsing to split on the first colon only

[iafuad]

This fixes the changedetectionio.store:get_all_headers_in_textfile_for_watch:559 - ERROR reading headers.txt at datastore/headers.txt too many values to unpack (expected 2) error if the headers contain URLs.

[dgtlmoon]

nice find!!!

please update this test before i can merge the fix

changedetection.io/changedetectionio/tests/test_request.py

Lines 378 to 380 in e799a1c

	with open('test-datastore/headers.txt', 'w') as f:
	f.write("global-header: nice\r\nnext-global-header: nice")

you should add an extra header there to check for

changedetection.io/changedetectionio/tests/test_request.py

Lines 408 to 412 in e799a1c

	assert b"Global-Header:nice" in res.data
	assert b"Next-Global-Header:nice" in res.data
	assert b"Xxx:ooo" in res.data
	assert b"Watch-Header:nice" in res.data
	assert b"Tag-Header:test" in res.data

[dgtlmoon]

Amazing, thank you so much