Allow setting paste title

[FliegendeWurst]

Fixes #90

Try a live version here https://paste.fliegendewurst.eu/dPmU6a.log

[matze]

From a cursory look, I like it but:

1. In light mode the deep black causes too much distracting contrast, in dark mode it's alright I'd say.
2. Even though the line is shortened when the window width becomes small it still causes a header bar that gets taller once it touches the buttons. At least on Firefox desktop and mobile.

[FliegendeWurst]

Point 2 fixed. Not sure how to properly solve (1). Switch to a gray color?

[matze]

Not sure how to properly solve (1). Switch to a gray color?

Lets go for font-weight: normal and color: #555.

[matze]

Looks good now! If you resolve the CSS conflict, I'll merge.

[matze]

Thanks again!