Fix few titles and headers

[RodionGork]

This is very simple, but good as exercise with github and pull-requests. So please leave it to others if you are less-or-more proficient with these things :)

There could be some pages with wrong titles (in <title> tag) and headers (in <h1>) tag. Wrong, meaning that they were copy-pasted from other pages. For example in 404 page and in task list. Perhaps somewhere else...

Please change these small snippets of text and create PR.