ArXiv fetcher support http url

[zesaro]

In this PR I wanted to fix the issue from koppor#328.
I simply used existing code in the same file which just takes the identifier at the end of the URL and perform a search.

For example: https://arxiv.org/abs/1802.01168 to 1802.01168

The error dialog does not appear anymore and a new entry is made.

---

• Change in CHANGELOG.md described
• Tests created for changes
• Manually tested changed features in running JabRef
• Screenshots added in PR description (for bigger UI changes)
• Ensured that the git commit message is a good one
• Check documentation status (Issue created for outdated help page at help.jabref.org?)

[tobiasdiez]

Thanks for your contribution. The code looks good to me. Can you please add a changelog entry and a test analogous to

jabref/src/test/java/org/jabref/logic/importer/fetcher/ArXivTest.java

Lines 161 to 164 in d8d3807

	@Test
	public void searchEntryByIdWith4Digits() throws Exception {
	assertEquals(Optional.of(sliceTheoremPaper), finder.performSearchById("1405.2249"));
	}

[Siedlerchr]

Yeah, looks good to me! I exactly had the same issue yesterday that I could not paste the whole url