Generate "ignore case" button on flamegraphs

[jputlock]

This feature is already implemented in the original perl script.

Changes:

• Adds an "ignore case" button to the top right of flamegraphs, shifting the search button left slightly
  • Added a tooltip for this, which forced direct use of the svg library instead of calling write_str
• Ctrl+i can be used to toggle this dynamically

"ignore case" is additionally bound into the URI parameters.

To verify, I ran cargo run --bin inferno-flamegraph < tests/data/flamegraph/base/flames.txt > test.svg and got the following flamegraph:

Hovering:

Searching final (standard behavior):

Searching final with ignore case: