Ignore does not work for file extensions

[krassowski]

To reproduce:

1. Create a markdown cell with text: "test.csv"
2. See csv highlighted as an unknown word
3. Try to ignore it from context menu
4. See that it gets added to ignore list as ".csv" but it does not get ignored after all

[ocordes]

Okay, I've checked this, there are two issues:

• .csv is added but only csv is highlighted, so we should only add words without leading/ending punctuations
• after any word is added we should trigger a recheck, then the word is correctly ignored.
• maybe it is wise to provide some default ignores which includes all file extensions ...