reduce weight of "boring" code lines such as import statements

[kantord]

things like an import statement can seem semantically highly relevant however they are unlikely to be what the user is looking for

these lines should probably not be completely hidden, especially if they are results of exact matches. however they could be given lower weight and conditionally hidden if there are more relevant results from the same file

also if they are the only result from a file, that file should have a very low weight compared to files that have it in 'real' code